## C++ || Multi Digit, Decimal & Negative Number Infix To Postfix Conversion & Evaluation

The following is sample code which demonstrates the implementation of a multi digit, decimal, and negative number infix to postfix converter and evaluator using a Finite State Machine

REQUIRED KNOWLEDGE FOR THIS PROGRAM

```How To Convert Infix To Postfix How To Evaluate A Postfix Expression What Is A Finite State Machine? ```

Using a Finite State Machine, the program demonstrated on this page has the ability to convert and evaluate a single digit, multi digit, decimal number, and/or negative number infix equation. So for example, if the the infix equation of (19.87 * ~2) was entered into the program, the converted postfix expression of 19.87 ~2* would display to the screen, as well as the final evaluated answer of -39.74.

NOTE: In this program, negative numbers are represented by the “~” symbol.

This program has the following flow of control:

```• Get an infix expression from the user • Convert the infix expression to postfix • Use a Finite State Machine to isolate all of the math operators, multi digit, decimal, negative and single digit numbers that are found in the postfix expression • Evaluate the postfix expression using the tokens found from the above step • Display the evaluated answer to the screen ```

The above steps are implemented below.

``` Multi Digit Infix To Postfix Conversion & Evaluation C++ // ============================================================================ // Author: K Perkins // Taken From: http://programmingnotes.org/ // Date: Jan 31, 2014 // File: InToPostEval.cpp // Description: The following demonstrates the implementation of an infix to // postfix converter and evaluator. Using a Finite State Machine, this // program has the ability to convert and evaluate multi digit, decimal, // negative and positive values. // ============================================================================ #include <iostream> #include <cstdlib> #include <cmath> #include <cctype> #include <string> #include <vector> #include <stack> using namespace std; /* This holds the transition states for our Finite State Machine -- They are placed in numerical order for easy understanding within the FSM array, which is located below */ enum FSM_TRANSITIONS { REJECT = 0, INTEGER, REAL, NEGATIVE, OPERATOR, UNKNOWN, SPACE }; /* This is the Finite State Machine -- The zero represents a place holder, so the row in the array starts on row 1 instead of 0 integer, real, negative, operator, unknown, space */ int stateTable[][7] = {{0, INTEGER, REAL, NEGATIVE, OPERATOR, UNKNOWN, SPACE}, /* STATE 1 */ {INTEGER, INTEGER, REAL, REJECT, REJECT, REJECT, REJECT}, /* STATE 2 */ {REAL, REAL, REJECT, REJECT, REJECT, REJECT, REJECT}, /* STATE 3 */ {NEGATIVE, INTEGER, REAL, REJECT, REJECT, REJECT, REJECT}, /* STATE 4 */ {OPERATOR, REJECT, REJECT, REJECT, REJECT, REJECT, REJECT}, /* STATE 5 */ {UNKNOWN, REJECT, REJECT, REJECT, REJECT, UNKNOWN, REJECT}, /* STATE 6 */ {SPACE, REJECT, REJECT, REJECT, REJECT, REJECT, REJECT}}; // function prototypes void DisplayDirections(); string ConvertInfixToPostfix(string infix); bool IsMathOperator(char token); int OrderOfOperations(char token); vector<string> Lexer(string postfix); int Get_FSM_Col(char& currentChar); double EvaluatePostfix(const vector<string>& postfix); double Calculate(char token, double op1, double op2); int main() { // declare variables string infix = ""; string postfix = ""; double answer = 0; vector<string> tokens; // display directions to user DisplayDirections(); // get data from user cout<<"\nPlease enter an Infix expression: "; getline(cin, infix); postfix = ConvertInfixToPostfix(infix); // use the "Lexer" function to isolate multi digit, negative and decimal // numbers, aswell as single digit numbers and math operators tokens = Lexer(postfix); // display the found tokens to the screen // for(unsigned x = 0; x < tokens.size(); ++x) // { // cout<<tokens.at(x)<<endl; // } cout <<"\nThe Infix expression = "<<infix; cout <<"\nThe Postfix expression = "<<postfix<<endl; answer = EvaluatePostfix(tokens); cout<<"\nFinal answer = "<<answer<<endl; return 0; }// end of main void DisplayDirections() {// this function displays instructions to the screen cout << "\n==== Infix To Postfix Conversion & Evaluation ====\n" <<"\nMath Operators:\n" <<"+ || Addition\n" <<"- || Subtraction\n" <<"* || Multiplication\n" <<"/ || Division\n" <<"% || Modulus\n" <<"^ || Power\n" <<"\$ || Square Root\n" <<"s || Sine\n" <<"c || Cosine\n" <<"t || Tangent\n" <<"~ || Negative Number\n" <<"Sample Infix Equation: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23))\n"; // ((sin(-4^5)*1.4)/(sqrt(23+2)--2.8))*(cos(1%2)/(7.28*.1987)^(tan(23))) }// end of DisplayDirections string ConvertInfixToPostfix(string infix) {// this function converts an infix expression to postfix // declare function variables string postfix; stack<char> charStack; // loop thru array until there is no more data for(unsigned x = 0; x < infix.length(); ++x) { // place numbers (standard, decimal, & negative) // numbers onto the 'postfix' string if((isdigit(infix[x])) || (infix[x] == '.') || (infix[x] == '~')) { postfix += infix[x]; } else if(isspace(infix[x])) { continue; } else if(IsMathOperator(infix[x])) { postfix += " "; // use the 'OrderOfOperations' function to check equality // of the math operator at the top of the stack compared to // the current math operator in the infix string while((!charStack.empty()) && (OrderOfOperations(charStack.top()) >= OrderOfOperations(infix[x]))) { // place the math operator from the top of the // stack onto the postfix string and continue the // process until complete postfix += charStack.top(); charStack.pop(); } // push the remaining math operator onto the stack charStack.push(infix[x]); } // push outer parentheses onto stack else if(infix[x] == '(') { charStack.push(infix[x]); } else if(infix[x] == ')') { // pop the current math operator from the stack while((!charStack.empty()) && (charStack.top() != '(')) { // place the math operator onto the postfix string postfix += charStack.top(); // pop the next operator from the stack and // continue the process until complete charStack.pop(); } if(!charStack.empty()) // pop '(' symbol off the stack { charStack.pop(); } else // no matching '(' { cout<<"\nPARENTHESES MISMATCH #1\n"; exit(1); } } else { cout<<"\nINVALID INPUT #1\n"; exit(1); } } // place any remaining math operators from the stack onto // the postfix array while(!charStack.empty()) { postfix += charStack.top(); charStack.pop(); } return postfix; }// end of ConvertInfixToPostfix bool IsMathOperator(char token) {// this function checks if operand is a math operator switch(tolower(token)) { case '+': case '-': case '*': case '/': case '%': case '^': case '\$': case 'c': case 's': case 't': return true; break; default: return false; break; } }// end of IsMathOperator int OrderOfOperations(char token) {// this function returns the priority of each math operator int priority = 0; switch(tolower(token)) { case 'c': case 's': case 't': priority = 5; break; case '^': case '\$': priority = 4; break; case '*': case '/': case '%': priority = 3; break; case '-': priority = 2; break; case '+': priority = 1; break; } return priority; }// end of OrderOfOperations vector<string> Lexer(string postfix) {// this function parses a postfix string using an FSM to generate // each individual token in the expression vector<string> tokens; char currentChar = ' '; int col = REJECT; int currentState = REJECT; string currentToken = ""; // use an FSM to parse multidigit and decimal numbers // also does error check for invalid input of decimals for(unsigned x = 0; x < postfix.length();) { currentChar = postfix[x]; // get the column number for the current character col = Get_FSM_Col(currentChar); // exit if the real number has multiple periods "." // in the expression (i.e: 19.3427.23) if((currentState == REAL) && (col == REAL)) { cerr<<"\nINVALID INPUT #2\n"; exit(1); } /* ======================================================== THIS IS WHERE WE CHECK THE FINITE STATE MACHINE TABLE USING THE "col" VARIABLE FROM ABOVE ^ ========================================================= */ // get the current state of our machine currentState = stateTable[currentState][col]; /* =================================================== THIS IS WHERE WE CHECK FOR A SUCESSFUL PARSE - If the current state in our machine == REJECT (the starting state), then we have sucessfully parsed a token, which is returned to its caller - ELSE we continue trying to find a sucessful token =================================================== */ if(currentState == REJECT) { if(currentToken != " ") // we dont care about whitespace { tokens.push_back(currentToken); } currentToken = ""; } else { currentToken += currentChar; ++x; } } // this ensures the last token gets saved when // we reach the end of the postfix string buffer if(currentToken != " ") // we dont care about whitespace { tokens.push_back(currentToken); } return tokens; }// end of Lexer int Get_FSM_Col(char& currentChar) {// this function determines the state of the type of character being examined // check for whitespace if(isspace(currentChar)) { return SPACE; } // check for integer numbers else if(isdigit(currentChar)) { return INTEGER; } // check for real numbers else if(currentChar == '.') { return REAL; } // check for negative numbers else if(currentChar == '~') { currentChar = '-'; return NEGATIVE; } // check for math operators else if(IsMathOperator(currentChar)) { return OPERATOR; } return UNKNOWN; }// end of Get_FSM_Col double EvaluatePostfix(const vector<string>& postfix) {// this function evaluates a postfix expression // declare function variables double op1 = 0; double op2 = 0; double answer = 0; stack<double> doubleStack; cout<<"\nCalculations:\n"; // loop thru array until there is no more data for(unsigned x = 0; x < postfix.size(); ++x) { // push numbers onto the stack if((isdigit(postfix[x][0])) || (postfix[x][0] == '.')) { doubleStack.push(atof(postfix[x].c_str())); } // push negative numbers onto the stack else if((postfix[x].length() > 1) && ((postfix[x][0] == '-') && (isdigit(postfix[x][1]) || (postfix[x][1] == '.')))) { doubleStack.push(atof(postfix[x].c_str())); } // if expression is a math operator, pop numbers from stack // & send the popped numbers to the 'Calculate' function else if(IsMathOperator(postfix[x][0]) && (!doubleStack.empty())) { char token = tolower(postfix[x][0]); // if expression is square root, sin, cos, // or tan operation only pop stack once if(token == '\$' || token == 's' || token == 'c' || token == 't') { op2 = 0; op1 = doubleStack.top(); doubleStack.pop(); answer = Calculate(token, op1, op2); doubleStack.push(answer); } else if(doubleStack.size() > 1) { op2 = doubleStack.top(); doubleStack.pop(); op1 = doubleStack.top(); doubleStack.pop(); answer = Calculate(token, op1, op2); doubleStack.push(answer); } } else // this should never execute, & if it does, something went really wrong { cout<<"\nINVALID INPUT #3\n"; exit(1); } } // pop the final answer from the stack, and return to main if(!doubleStack.empty()) { answer = doubleStack.top(); } return answer; }// end of EvaluatePostfix double Calculate(char token, double op1, double op2) {// this function carries out the actual math process double ans = 0; switch(tolower(token)) { case '+': cout<<op1<<token<<op2<<" = "; ans = op1 + op2; break; case '-': cout<<op1<<token<<op2<<" = "; ans = op1 - op2; break; case '*': cout<<op1<<token<<op2<<" = "; ans = op1 * op2; break; case '/': cout<<op1<<token<<op2<<" = "; ans = op1 / op2; break; case '%': cout<<op1<<token<<op2<<" = "; ans = ((int)op1%(int)op2)+modf(op1 , &op2); break; case '^': cout<<op1<<token<<op2<<" = "; ans = pow(op1, op2); break; case '\$': cout<<char(251)<<op1<<" = "; ans = sqrt(op1); break; case 'c': cout<<"cos("<<op1<<") = "; ans = cos(op1); break; case 's': cout<<"sin("<<op1<<") = "; ans = sin(op1); break; case 't': cout<<"tan("<<op1<<") = "; ans = tan(op1); break; default: ans = 0; break; } cout<<ans<<endl; return ans; }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454 // ============================================================================//   Author:  K Perkins//   Taken From: http://programmingnotes.org///   Date:  Jan 31, 2014//   File: InToPostEval.cpp//   Description: The following demonstrates the implementation of an infix to//     postfix converter and evaluator. Using a Finite State Machine, this//     program has the ability to convert and evaluate multi digit, decimal,//     negative and positive values.// ============================================================================#include <iostream>#include <cstdlib>#include <cmath>#include <cctype>#include <string>#include <vector>#include <stack>using namespace std; /* This holds the transition states for our Finite State Machine    -- They are placed in numerical order for easy understanding within     the FSM array, which is located below */ enum FSM_TRANSITIONS{    REJECT = 0,    INTEGER,    REAL,    NEGATIVE,    OPERATOR,    UNKNOWN,    SPACE}; /* This is the Finite State Machine    -- The zero represents a place holder, so the row in the array         starts on row 1 instead of 0                            integer,  real,  negative, operator, unknown, space */int stateTable[][7] = {{0, INTEGER,  REAL, NEGATIVE, OPERATOR,  UNKNOWN,  SPACE},/* STATE 1 */   {INTEGER,  INTEGER,  REAL,   REJECT,  REJECT,   REJECT,  REJECT},/* STATE 2 */   {REAL,       REAL,  REJECT,  REJECT,  REJECT,   REJECT,  REJECT},/* STATE 3 */   {NEGATIVE, INTEGER,  REAL,   REJECT,  REJECT,   REJECT,  REJECT},/* STATE 4 */   {OPERATOR,  REJECT, REJECT,  REJECT,  REJECT,   REJECT,  REJECT},/* STATE 5 */   {UNKNOWN,   REJECT, REJECT,  REJECT,  REJECT,   UNKNOWN, REJECT},/* STATE 6 */   {SPACE,     REJECT, REJECT,  REJECT,  REJECT,   REJECT,  REJECT}}; // function prototypesvoid DisplayDirections();string ConvertInfixToPostfix(string infix);bool IsMathOperator(char token);int OrderOfOperations(char token);vector<string> Lexer(string postfix);int Get_FSM_Col(char& currentChar);double EvaluatePostfix(const vector<string>& postfix);double Calculate(char token, double op1, double op2); int main(){    // declare variables    string infix = "";    string postfix = "";    double answer = 0;    vector<string> tokens;     // display directions to user    DisplayDirections();     // get data from user    cout<<"\nPlease enter an Infix expression: ";    getline(cin, infix);     postfix = ConvertInfixToPostfix(infix);     // use the "Lexer" function to isolate multi digit, negative and decimal    // numbers, aswell as single digit numbers and math operators    tokens = Lexer(postfix);     // display the found tokens to the screen// for(unsigned x = 0; x < tokens.size(); ++x)// {//     cout<<tokens.at(x)<<endl;// }     cout <<"\nThe Infix expression = "<<infix;    cout <<"\nThe Postfix expression = "<<postfix<<endl;     answer = EvaluatePostfix(tokens);     cout<<"\nFinal answer = "<<answer<<endl;     return 0;}// end of main void DisplayDirections(){// this function displays instructions to the screen    cout << "\n==== Infix To Postfix Conversion & Evaluation ====\n"        <<"\nMath Operators:\n"        <<"+ || Addition\n"        <<"- || Subtraction\n"        <<"* || Multiplication\n"        <<"/ || Division\n"        <<"% || Modulus\n"        <<"^ || Power\n"        <<"\$ || Square Root\n"        <<"s || Sine\n"        <<"c || Cosine\n"        <<"t || Tangent\n"        <<"~ || Negative Number\n"        <<"Sample Infix Equation: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23))\n";        // ((sin(-4^5)*1.4)/(sqrt(23+2)--2.8))*(cos(1%2)/(7.28*.1987)^(tan(23)))}// end of DisplayDirections string ConvertInfixToPostfix(string infix){// this function converts an infix expression to postfix    // declare function variables    string postfix;    stack<char> charStack;     // loop thru array until there is no more data    for(unsigned x = 0; x < infix.length(); ++x)    {        // place numbers (standard, decimal, & negative)        // numbers onto the 'postfix' string        if((isdigit(infix[x])) || (infix[x] == '.') || (infix[x] == '~'))        {            postfix += infix[x];        }        else if(isspace(infix[x]))        {            continue;        }        else if(IsMathOperator(infix[x]))        {            postfix += " ";            // use the 'OrderOfOperations' function to check equality            // of the math operator at the top of the stack compared to            // the current math operator in the infix string            while((!charStack.empty()) &&                (OrderOfOperations(charStack.top()) >= OrderOfOperations(infix[x])))            {                // place the math operator from the top of the                // stack onto the postfix string and continue the                // process until complete                postfix += charStack.top();                charStack.pop();            }            // push the remaining math operator onto the stack            charStack.push(infix[x]);        }        // push outer parentheses onto stack        else if(infix[x] == '(')        {            charStack.push(infix[x]);        }        else if(infix[x] == ')')        {            // pop the current math operator from the stack            while((!charStack.empty()) && (charStack.top() != '('))            {                // place the math operator onto the postfix string                postfix += charStack.top();                // pop the next operator from the stack and                // continue the process until complete                charStack.pop();            }             if(!charStack.empty()) // pop '(' symbol off the stack            {                charStack.pop();            }            else // no matching '('            {                cout<<"\nPARENTHESES MISMATCH #1\n";                exit(1);            }        }        else        {            cout<<"\nINVALID INPUT #1\n";            exit(1);        }    }     // place any remaining math operators from the stack onto    // the postfix array    while(!charStack.empty())    {        postfix += charStack.top();        charStack.pop();    }     return postfix;}// end of ConvertInfixToPostfix bool IsMathOperator(char token){// this function checks if operand is a math operator    switch(tolower(token))    {        case '+': case '-': case '*': case '/':        case '%': case '^': case '\$': case 'c':        case 's': case 't':            return true;            break;        default:           return false;           break;    }}// end of IsMathOperator int OrderOfOperations(char token){// this function returns the priority of each math operator    int priority = 0;    switch(tolower(token))    {        case 'c': case 's': case 't':           priority = 5;           break;        case '^': case '\$':           priority = 4;           break;        case '*': case '/': case '%':           priority = 3;           break;        case '-':           priority = 2;           break;        case '+':           priority = 1;           break;    }    return priority;}// end of OrderOfOperations vector<string> Lexer(string postfix){// this function parses a postfix string using an FSM to generate //  each individual token in the expression    vector<string> tokens;    char currentChar = ' ';    int col = REJECT;    int currentState = REJECT;    string currentToken = "";     // use an FSM to parse multidigit and decimal numbers    // also does error check for invalid input of decimals    for(unsigned x = 0; x < postfix.length();)    {        currentChar = postfix[x];         // get the column number for the current character        col = Get_FSM_Col(currentChar);         // exit if the real number has multiple periods "."        // in the expression (i.e: 19.3427.23)        if((currentState == REAL) && (col == REAL))        {            cerr<<"\nINVALID INPUT #2\n";            exit(1);        }        /* ========================================================             THIS IS WHERE WE CHECK THE FINITE STATE MACHINE TABLE               USING THE "col" VARIABLE FROM ABOVE ^           ========================================================= */         // get the current state of our machine        currentState = stateTable[currentState][col];         /* ===================================================           THIS IS WHERE WE CHECK FOR A SUCESSFUL PARSE           - If the current state in our machine == REJECT             (the starting state), then we have sucessfully parsed             a token, which is returned to its caller             - ELSE we continue trying to find a sucessful token             =================================================== */        if(currentState == REJECT)        {            if(currentToken != " ") // we dont care about whitespace            {                tokens.push_back(currentToken);            }            currentToken = "";        }        else        {            currentToken += currentChar;            ++x;        }     }    // this ensures the last token gets saved when    // we reach the end of the postfix string buffer    if(currentToken != " ") // we dont care about whitespace    {        tokens.push_back(currentToken);    }    return tokens;}// end of Lexer int Get_FSM_Col(char& currentChar){// this function determines the state of the type of character being examined    // check for whitespace    if(isspace(currentChar))    {        return SPACE;    }     // check for integer numbers    else if(isdigit(currentChar))    {        return INTEGER;    }     // check for real numbers    else if(currentChar == '.')    {        return REAL;    }     // check for negative numbers    else if(currentChar == '~')    {        currentChar = '-';        return NEGATIVE;    }     // check for math operators    else if(IsMathOperator(currentChar))    {        return OPERATOR;    }    return UNKNOWN;}// end of Get_FSM_Col double EvaluatePostfix(const vector<string>& postfix){// this function evaluates a postfix expression    // declare function variables    double op1 = 0;    double op2 = 0;    double answer = 0;    stack<double> doubleStack;     cout<<"\nCalculations:\n";     // loop thru array until there is no more data    for(unsigned x = 0; x < postfix.size(); ++x)    {        // push numbers onto the stack        if((isdigit(postfix[x][0])) || (postfix[x][0] == '.'))        {           doubleStack.push(atof(postfix[x].c_str()));        }        // push negative numbers onto the stack        else if((postfix[x].length() > 1) && ((postfix[x][0] == '-') &&            (isdigit(postfix[x][1]) || (postfix[x][1] == '.'))))        {           doubleStack.push(atof(postfix[x].c_str()));        }        // if expression is a math operator, pop numbers from stack        // & send the popped numbers to the 'Calculate' function        else if(IsMathOperator(postfix[x][0]) && (!doubleStack.empty()))        {            char token = tolower(postfix[x][0]);             // if expression is square root, sin, cos,            // or tan operation only pop stack once            if(token == '\$' || token == 's' || token == 'c' || token == 't')            {                op2 = 0;                op1 = doubleStack.top();                doubleStack.pop();                answer = Calculate(token, op1, op2);                doubleStack.push(answer);            }            else if(doubleStack.size() > 1)            {                op2 = doubleStack.top();                doubleStack.pop();                op1 = doubleStack.top();                doubleStack.pop();                answer = Calculate(token, op1, op2);                doubleStack.push(answer);            }        }        else // this should never execute, & if it does, something went really wrong        {           cout<<"\nINVALID INPUT #3\n";           exit(1);        }    }    // pop the final answer from the stack, and return to main    if(!doubleStack.empty())    {        answer = doubleStack.top();    }    return answer;}// end of EvaluatePostfix double Calculate(char token, double op1, double op2){// this function carries out the actual math process    double ans = 0;    switch(tolower(token))    {        case '+':           cout<<op1<<token<<op2<<" = ";           ans = op1 + op2;           break;        case '-':           cout<<op1<<token<<op2<<" = ";           ans = op1 - op2;           break;        case '*':           cout<<op1<<token<<op2<<" = ";           ans = op1 * op2;           break;        case '/':           cout<<op1<<token<<op2<<" = ";           ans = op1 / op2;           break;        case '%':           cout<<op1<<token<<op2<<" = ";           ans = ((int)op1%(int)op2)+modf(op1 , &op2);           break;        case '^':           cout<<op1<<token<<op2<<" = ";           ans = pow(op1, op2);           break;        case '\$':           cout<<char(251)<<op1<<" = ";           ans = sqrt(op1);           break;        case 'c':            cout<<"cos("<<op1<<") = ";            ans = cos(op1);            break;        case 's':            cout<<"sin("<<op1<<") = ";            ans = sin(op1);            break;        case 't':            cout<<"tan("<<op1<<") = ";            ans = tan(op1);            break;        default:           ans = 0;           break;    }    cout<<ans<<endl;    return ans;}// http://programmingnotes.org/ ```

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

The following is sample output.

```====== RUN 1 ====== ==== Infix To Postfix Conversion & Evaluation ====```

``` Math Operators: + || Addition - || Subtraction * || Multiplication / || Division % || Modulus ^ || Power \$ || Square Root s || Sine c || Cosine t || Tangent ~ || Negative Number Sample Infix Equation: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23)) Please enter an Infix expression: 12/3*9 The Infix expression = 12/3*9 The Postfix expression = 12 3 /9* Calculations: 12/3 = 4 4*9 = 36 Final answer = 36 ====== RUN 2 ====== ==== Infix To Postfix Conversion & Evaluation ==== Math Operators: + || Addition - || Subtraction * || Multiplication / || Division % || Modulus ^ || Power \$ || Square Root s || Sine c || Cosine t || Tangent ~ || Negative Number Sample Infix Equation: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23)) Please enter an Infix expression: ~150.89996 - 87.56643 The Infix expression = ~150.89996 - 87.56643 The Postfix expression = ~150.89996 87.56643- Calculations: -150.9-87.5664 = -238.466 Final answer = -238.466 ====== RUN 3 ====== ==== Infix To Postfix Conversion & Evaluation ==== Math Operators: + || Addition - || Subtraction * || Multiplication / || Division % || Modulus ^ || Power \$ || Square Root s || Sine c || Cosine t || Tangent ~ || Negative Number Sample Infix Equation: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23)) Please enter an Infix expression: ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23)) The Infix expression = ((s(~4^5)*1.4)/(\$(23+2)-~2.8))*(c(1%2)/(7.28*.1987)^(t23)) The Postfix expression = ~4 5^ s1.4* 23 2+ \$~2.8-/ 1 2% c7.28 .1987* 23t^/* Calculations: -4^5 = -1024 sin(-1024) = 0.158533 0.158533*1.4 = 0.221947 23+2 = 25 √25 = 5 5--2.8 = 7.8 0.221947/7.8 = 0.0284547 1%2 = 1 cos(1) = 0.540302 7.28*0.1987 = 1.44654 tan(23) = 1.58815 1.44654^1.58815 = 1.79733 0.540302/1.79733 = 0.300614 0.0284547*0.300614 = 0.00855389 Final answer = 0.00855389 ```

## Python || Random Number Guessing Game Using Random MyRNG & While Loop

Here is another homework assignment which was presented in introduction class. The following is a simple guessing game using commandline arguments, which demonstrates the use of generating random numbers.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

```How To Get User Input Getting Commandline Arguments While Loops MyRNG.py - Random Number Class ```

==== 1. DESCRIPTION ====

The following program is a simple guessing game which demonstrates how to generate random numbers using python. This program will seed the random number generator (located in the file MyRNG.py), select a number at random, and then ask the user for a guess. Using a while loop, the user will keep attempting to guess the selected random number until the correct guess is obtained, afterwhich the user will have the option of continuing play or exiting.

==== 2. USAGE ====

The user enters various options into the program via the commandline. An example of how the commandline can be used is given below.

``` python3 guess.py [-h] [-v] -s [seed] -m 2 -M 353 ```

Where the brackets are meant to represent features which are optional, meaning the user does not have to specify them at run time.

The -m and -M options are mandatory.

• -M is best picked as a large prime integer
• -m is best picked as an integer in the range of 2,3,..,M-1

NOTE: The use of commandline arguments is not mandatory. If any of the mandatory options are not selected, the program uses its own logic to generate random numbers.

==== 3. FEATURES ====

The following lists and explains the command line argument options.

-s (seed): Seed takes an integer as a parameter and is used to seed the random number generator. When omitted, the program uses its own logic to seed the generator

-v (verbose): Turn on debugging messages.

-h (help): Print out a help message which tells the user how to run the program and a brief description of the program.

-m (minimum): Set the minimum of the range of numbers the program will select its numbers from.

-M (maximum): Set the maximum of the range of numbers the program will select its numbers from.

``` I'm Thinking of a Number Between 1 and 1000... Python # ============================================================================= # Name: K Perkins # Date: Aug 6, 2013 # Taken From: http://programmingnotes.org/ # File: guess.py # Description: This is the guess.py module which uses a random number # generator to simulate a simple guessing game. This program will seed the # random number generator (located in the file MyRNG.py), select a number at # random, and then ask the user for a guess. The user will keep attempting # to guess the selected random number until the correct guess is obtained, # afterwhich the user will have the option of continuing play or exiting # ============================================================================= # Sample commandline: guess.py -s 3454 -m 1 -M 1000 import sys, pdb from MyRNG import * def Usage(status, msg = ""): # Function prints out usage directions aswell as a simple # message if a string is sent as a 2nd parameter if(msg): print(msg) print("nUSAGE:n ", sys.argv[0],"[-h help] [-v] [-s seed] [-m minimum number]", "[-M maximum number]") sys.exit(status) def IsWarmer(userGuess, numGuess, randomNumber): # Function determines if the current number the user guesses is closer # to the random number than the previous guess. # Function returns TRUE if current user guess is 'warmer' # than previous, otherwise returns FALSE currGuessDifference = userGuess[numGuess] - randomNumber currGuessDifference = math.fabs(currGuessDifference) prevGuessDifference = userGuess[numGuess-1] - randomNumber prevGuessDifference = math.fabs(prevGuessDifference) if(currGuessDifference < prevGuessDifference): return True else: return False def main(): # This is the 'main' function which first takes a string via the commandline # and parses it to determine various modes of operation, namely being # 'seed,' 'minimum,' and 'maximum.' After the commandline options # are obtained, that information is sent to the MyRNG class in order # to generate a random number. After a random number is found, using # a while loop, the user is prompted to try and guess that specified # number, repeatedly doing so until a correct guess is found # declare variables index = 0 # counter which is used to index the sys.argv string verbose = False choices = (("y"),("yes"),("n"),("no")) # This is to be used for the while loop seed = 806189064 # saves the seed from the command line minimum = 1 # saves the minimum num from the command line maximum = 1000 # saves the maximum num from the command line loop = True # this controls the while loop randomNumber = 0 # this saves the random number from the generator userGuess = [] # this saves the user guesses numGuess = 0 # this is the counter wgich keeps track of the num of usr guesses newGame = True # bool to determine if the user is playing a new game programDescr = """nDESCRIPTION: The following is a simple guessing game in which the user is prompted to guess a number and the computer determines if the guess is above, below or exactly the random number which was selected.""" # == determine if the user entered enough args via commandline == # if(len(sys.argv) < 1): #if not enough args, stop the program and print an error message Usage(1, "n** Must provide atleast 1 argument") # == parse thru the argv string to find the appropriate tokens == # for currentArg in sys.argv: if(currentArg == "-h"): # print out the usage message and exit. Usage(2, programDescr) elif(currentArg == "-v"): # set verbose mode to be true for debugging messages verbose = True elif(currentArg == "-s"): # set the seed here # if the user doesnt specify a seed, the # default is my CWID if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())): seed = int(sys.argv[index+1]) else: seed = 806189064 elif currentArg == "-m": # set the minimum here # if the user doesnt specify a min, the default is 1 if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())): minimum = int(sys.argv[index+1]) else: minimum = 1 elif currentArg == "-M": # set the maximum here # if the user doesnt specify a max, the default is 1000 if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())): maximum = int(sys.argv[index+1]) else: maximum = 1000 # increment the index counter index += 1 # print debugging messages if debug mode is on if(verbose): print ("nThis message only appears if verbose mode is turned on.") print (""" ** To continue seeing debugging messages, press the "n" button when prompted. To print the current value of variables, press the "p" button followed by the name of the variable you wish to print. Press the "l" button to visually see where you are in the programs souce code. To quit debugging, press the "c" button.n""") pdb.set_trace() print("nSeed = %d, Minimum = %d, Maximum = %d" %(seed, minimum, maximum)) # == declare the class object == # random = MyRNG(minimum, maximum) random.Seed(seed) randomNumber = random.Next() print("nI'm thinking of a number between %d and %d" ". Go ahead and make your first guess. " %(minimum, maximum)) # * this is the while loop which simulates a guessing game. # * the loop gets a number from the user and determines if the # user input is a "winner, warmer, or colder" in relation to the # random number which was generated. # * once the user guesses correctly, they have a choice of continuing # play or exiting the game. If they choose to play again, a new # random number is generated while(loop): userGuess.append(int(input(">> "))) if(newGame): newGame = False if((userGuess[numGuess] > randomNumber) or (userGuess[numGuess] < randomNumber)): print("nSorry that was not correct, please try again...n") elif((userGuess[numGuess] > randomNumber) or (userGuess[numGuess] < randomNumber)): if(IsWarmer(userGuess, numGuess, randomNumber)): print("nWARMERn") else: print("nCOLDERn") if(userGuess[numGuess] == randomNumber): print("nWINNER! You have guessed correctly!") print("It took you %d attempt(s) to find the answer!" %(numGuess+1)) del userGuess[:] numGuess = -1 answer = input("nWould you like to play again? (Yes or No): ") answer = answer.lower() if(answer in choices[:2]): randomNumber = random.Next() print("nMake a guess between %d and %dn" %(minimum, maximum)) newGame = True elif((answer in choices[2:]) or (answer not in choices[2:])): loop = False numGuess += 1 print("nThanks for playing!!") if __name__ == "__main__": main() # http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168 # =============================================================================#   Name:  K Perkins#   Date:   Aug 6, 2013#   Taken From: http://programmingnotes.org/#   File: guess.py#   Description: This is the guess.py module which uses a random number#    generator to simulate a simple guessing game. This program will seed the#    random number generator (located in the file MyRNG.py), select a number at#    random, and then ask the user for a guess. The user will keep attempting#    to guess the selected random number until the correct guess is obtained,#    afterwhich the user will have the option of continuing play or exiting# =============================================================================# Sample commandline: guess.py -s 3454 -m 1 -M 1000import sys, pdbfrom MyRNG import * def Usage(status, msg = ""):    #   Function prints out usage directions aswell as a simple    #        message if a string is sent as a 2nd parameter    if(msg):        print(msg)    print("nUSAGE:n    ",           sys.argv[0],"[-h help] [-v] [-s seed] [-m minimum number]",            "[-M maximum number]")    sys.exit(status) def IsWarmer(userGuess, numGuess, randomNumber):    #   Function determines if the current number the user guesses is closer    #       to the random number than the previous guess.    #       Function returns TRUE if current user guess is 'warmer'    #       than previous, otherwise returns FALSE    currGuessDifference = userGuess[numGuess] - randomNumber    currGuessDifference = math.fabs(currGuessDifference)    prevGuessDifference = userGuess[numGuess-1] - randomNumber    prevGuessDifference = math.fabs(prevGuessDifference)     if(currGuessDifference < prevGuessDifference):        return True    else:        return False def main():#   This is the 'main' function which first takes a string via the commandline#        and parses it to determine various modes of operation, namely being#        'seed,' 'minimum,' and 'maximum.' After the commandline options#        are obtained, that information is sent to the MyRNG class in order#        to generate a random number. After a random number is found, using#        a while loop, the user is prompted to try and guess that specified#        number, repeatedly doing so until a correct guess is found     # declare variables    index = 0   # counter which is used to index the sys.argv string    verbose = False    choices = (("y"),("yes"),("n"),("no"))  # This is to be used for the while loop    seed = 806189064  # saves the seed from the command line    minimum = 1  # saves the minimum num from the command line    maximum = 1000  # saves the maximum num from the command line    loop = True  # this controls the while loop    randomNumber = 0  # this saves the random number from the generator    userGuess = []  # this saves the user guesses    numGuess = 0  # this is the counter wgich keeps track of the num of usr guesses    newGame = True # bool to determine if the user is playing a new game    programDescr = """nDESCRIPTION:          The following is a simple guessing game in which the user         is prompted to guess a number and the computer determines         if the guess is above, below or exactly the random number         which was selected."""    # == determine if the user entered enough args via commandline == #    if(len(sys.argv) < 1):        #if not enough args, stop the program and print an error message        Usage(1, "n** Must provide atleast 1 argument")     # == parse thru the argv string to find the appropriate tokens == #    for currentArg in sys.argv:        if(currentArg == "-h"):        # print out the usage message and exit.            Usage(2, programDescr)        elif(currentArg == "-v"):        # set verbose mode to be true for debugging messages            verbose = True        elif(currentArg == "-s"):        # set the seed here        # if the user doesnt specify a seed, the        # default is my CWID            if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())):                seed = int(sys.argv[index+1])            else:                seed = 806189064        elif currentArg == "-m":        # set the minimum here        # if the user doesnt specify a min, the default is 1            if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())):                minimum = int(sys.argv[index+1])            else:                minimum = 1        elif currentArg == "-M":        # set the maximum here        # if the user doesnt specify a max, the default is 1000            if((index+1 < len(sys.argv)) and (sys.argv[index+1].isdigit())):                maximum = int(sys.argv[index+1])            else:                maximum = 1000        # increment the index counter        index += 1     # print debugging messages if debug mode is on    if(verbose):        print ("nThis message only appears if verbose mode is turned on.")        print ("""           ** To continue seeing debugging messages, press the "n"           button when prompted. To print the current value of variables,           press the "p" button followed by the name of the variable you           wish to print. Press the "l" button to visually see where you           are in the programs souce code. To quit debugging, press the           "c" button.n""")        pdb.set_trace()     print("nSeed = %d, Minimum = %d, Maximum = %d" %(seed, minimum, maximum))     # == declare the class object == #    random = MyRNG(minimum, maximum)    random.Seed(seed)    randomNumber = random.Next()     print("nI'm thinking of a number between %d and %d"      ". Go ahead and make your first guess. " %(minimum, maximum))     # * this is the while loop which simulates a guessing game.    # * the loop gets a number from the user and determines if the    # user input is a "winner, warmer, or colder" in relation to the    # random number which was generated.    # * once the user guesses correctly, they have a choice of continuing    # play or exiting the game. If they choose to play again, a new    # random number is generated    while(loop):        userGuess.append(int(input(">> ")))         if(newGame):            newGame = False            if((userGuess[numGuess] > randomNumber) or (userGuess[numGuess] < randomNumber)):                print("nSorry that was not correct, please try again...n")        elif((userGuess[numGuess] > randomNumber) or (userGuess[numGuess] < randomNumber)):            if(IsWarmer(userGuess, numGuess, randomNumber)):                print("nWARMERn")            else:                print("nCOLDERn")        if(userGuess[numGuess] == randomNumber):            print("nWINNER! You have guessed correctly!")            print("It took you %d attempt(s) to find the answer!" %(numGuess+1))            del userGuess[:]            numGuess = -1            answer = input("nWould you like to play again? (Yes or No): ")            answer = answer.lower()            if(answer in choices[:2]):                randomNumber = random.Next()                print("nMake a guess between %d and %dn" %(minimum, maximum))                newGame = True            elif((answer in choices[2:]) or (answer not in choices[2:])):                loop = False        numGuess += 1     print("nThanks for playing!!") if __name__ == "__main__":    main()# http://programmingnotes.org/ ```

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output:

`Seed = 806189064, Minimum = 1, Maximum = 1000`

``` I'm thinking of a number between 1 and 1000. Go ahead and make your first guess. >> 500 Sorry that was not correct, please try again... >> 400 WARMER >> 600 COLDER >> 300 WARMER >> 150 WARMER >> 100 COLDER >> 180 COLDER >> 190 COLDER >> 130 WARMER >> 128 WINNER! You have guessed correctly! It took you 10 attempt(s) to find the answer! Would you like to play again? (Yes or No): y ------------------------------------------------------------ Make a guess between 1 and 1000 >> 500 Sorry that was not correct, please try again... >> 600 COLDER >> 400 WARMER >> 300 WARMER >> 280 WARMER >> 260 WARMER >> 250 COLDER >> 256 WINNER! You have guessed correctly! It took you 8 attempt(s) to find the answer! Would you like to play again? (Yes or No): n ```

```Thanks for playing!! ```

## C++ || Custom Template Hash Map With Iterator Using Separate Chaining

Before we get into the code, what is a Hash Map? Simply put, a Hash Map is an extension of a Hash Table; which is a data structure used to map unique “keys” to specific “values.” The Hash Map demonstrated on this page is different from the previous Hash Table implementation in that key/value pairs do not need to be the same datatype, they can be completely different. So for example, if you wish to map a string “key” to an integer “value“, utilizing a Hash Map is ideal.

In its most simplest form, a Hash Map can be thought of as an associative array, or a “dictionary.” Hash Map’s are composed of a collection of key/value pairs, such that each possible key appears atleast once in the collection for a given value. While a standard array requires that indice subscripts be integers, a hash map can use a string, an integer, or even a floating point value as the index. That index is called the “key,” and the contents within the array at that specific index location is called the “value.” A hash map uses a hash function to generate an index into the table, creating buckets or slots, from which the correct value can be found.

To illustrate, suppose that you’re working with some data that has values associated with strings — for instance, you might have student names and you wish to assign them grades. How would you store this data? Depending on your skill level, you might use multiple arrays during the implementation. For example, in terms of a one dimensional array, if we wanted to access the data for a student located at index #25, we could access it by doing:

``` studentNames[25]; // do something with the data studentGrades[25]; ```

Here, we dont have to search through each element in the array to find what we need, we just access it at index #25. The question is, how do we know that index #25 holds the data that we are looking for? If we have a large set of data, not only will keeping track of multiple arrays become tiresome, but doing a sequential search over each item within the separate arrays can become very inefficient. That is where hashing comes in handy. Using a Hash Map, we can use the students name as the “key,” and the students grade as the data “value.” Given this “key” (the students name), we can apply a hash function to map a unique index or bucket within the hash table to find the data “value” (the students grade) that we wish to access.

So in essence, a Hash Map is an extension of a hash table, which is a data structure that stores key/value pairs. Hash tables are typically used because they are ideal for doing a quick search of items.

Though hashing is ideal, it isnt perfect. It is possible for multiple “keys” to be hashed into the same location. Hash “collisions” are practically unavoidable when hashing large data sets. The code demonstrated on this page handles collisions via separate chaining, utilizing an array of linked list head nodes to store multiple keys within one bucket – should any collisions occur.

A special feature of this current hash map class is that its implemented as a multimap, meaning that more than one “value” can be associated with a given “key.” For example, in a student enrollment system where students may be enrolled in multiple classes simultaneously, there might be an association for each enrollment where the “key” is the student ID, and the “value” is the course ID. In this example, if a given student is enrolled in three courses, there will be three associated “values” (course ID’s) for one “key” (student ID) in the Hash Map.

An iterator was also implemented, making data access that much more simple within the hash map class. Click here for an overview demonstrating how custom iterators can be built.

=== CUSTOM TEMPLATE HASH MAP WITH ITERATOR ===

``` #include 'HashMap.h' - Hash Map With Iterator C++ // ============================================================================ // Author: K Perkins // Date: June 11, 2013 // Taken From: http://programmingnotes.org/ // File: HashMap.h // Description: This is a class which implements various functions // demonstrating the use of a Hash Map. // ============================================================================ #ifndef TEMPLATE_HASH_MAP #define TEMPLATE_HASH_MAP #include <iostream> #include <string> #include <sstream> #include <cstdlib> // if user doesnt define, this is the // default hash map size const int HASH_SIZE = 350; template <class Key, class Value> class HashMap { public: HashMap(int hashSze = HASH_SIZE); /* Function: Constructor initializes hash map Precondition: None Postcondition: Defines private variables */ bool IsEmpty(int keyIndex); /* Function: Determines whether hash map is empty at the given hash map key index Precondition: Hash map has been created Postcondition: The function = true if the hash map is empty and the function = false if hash map is not empty */ bool IsFull(); /* Function: Determines whether hash map is full Precondition: Hash map has been created Postcondition: The function = true if the hash map is full and the function = false if hash map is not full */ int Hash(Key m_key); /* Function: Computes and returns a hash map key index for a given item The returned key index is the given cell where the item resides Precondition: Hash map has been created and is not full Postcondition: The hash key is returned */ void Insert(Key m_key, Value m_value); /* Function: Adds new item to the back of the list at a given key in the hash map A unique hash key is automatically generated for each new item Precondition: Hash map has been created and is not full Postcondition: Item is in the hash map */ bool Remove(Key m_key, Value deleteItem); /* Function: Removes the first instance from the map whose value is "deleteItem" Precondition: Hash map has been created and is not empty Postcondition: The function = true if deleteItem is found and the function = false if deleteItem is not found */ void Sort(int keyIndex); /* Function: Sort the items in the map at the given hashmap key index Precondition: Hash map has been initialized Postcondition: The hash map is sorted */ int TableSize(); /* Function: Return the size of the hash map Precondition: Hash map has been initialized Postcondition: The size of the hash map is returned */ int TotalElems(); /* Function: Return the total number of elements contained in the hash map Precondition: Hash map has been initialized Postcondition: The size of the hash map is returned */ int BucketSize(int keyIndex); /* Function: Return the number of items contained in the hash map cell at the given hashmap key index Precondition: Hash map has been initialized Postcondition: The size of the given key cell is returned */ int Count(Key m_key, Value searchItem); /* Function: Return the number of times searchItem appears in the map at the given key Precondition: Hash map has been initialized Postcondition: The number of times searchItem appears in the map is returned */ int ContainsKey(Key m_key); /* Function: Return the number of times the given key appears in the hashmap Precondition: Hash map has been initialized Postcondition: The number of times the given key appears in the map is returned */ void MakeEmpty(); /* Function: Initializes hash map to an empty state Precondition: Hash map has been created Postcondition: Hash map no longer exists */ ~HashMap(); /* Function: Removes the hash map Precondition: Hash map has been declared Postcondition: Hash map no longer exists */ // -- ITERATOR CLASS -- class Iterator; /* Function: Class declaration to the iterator Precondition: Hash map has been declared Postcondition: Hash Iterator has been declared */ Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;} /* Function: Returns the beginning of the current hashmap key index Precondition: Hash map has been declared Postcondition: Hash cell has been returned to the Iterator */ Iterator end(int keyIndex=0){return NULL;} /* Function: Returns the end of the current hashmap key index Precondition: Hash map has been declared Postcondition: Hash cell has been returned to the Iterator */ private: struct KeyValue // struct to hold key/value pairs { Key key; Value value; }; struct node { KeyValue currentItem; node* next; }; node** head; // array of linked list declaration - front of each hash map cell int hashSize; // the size of the hash map (how many cells it has) int totElems; // holds the total number of elements in the entire table int* bucketSize; // holds the total number of elems in each specific hash map cell }; //========================= Implementation ================================// template <class Key, class Value> HashMap<Key, Value>::HashMap(int hashSze) { hashSize = hashSze; head = new node*[hashSize]; bucketSize = new int[hashSize]; for(int x=0; x < hashSize; ++x) { head[x] = NULL; bucketSize[x] = 0; } totElems = 0; }/* End of HashMap */ template <class Key, class Value> bool HashMap<Key, Value>::IsEmpty(int keyIndex) { if(keyIndex >=0 && keyIndex < hashSize) { return head[keyIndex] == NULL; } return true; }/* End of IsEmpty */ template <class Key, class Value> bool HashMap<Key, Value>::IsFull() { try { node* location = new node; delete location; return false; } catch(std::bad_alloc&) { return true; } }/* End of IsFull */ template <class Key, class Value> int HashMap<Key, Value>::Hash(Key m_key) { long h = 19937; std::stringstream convert; // convert the parameter to a string using "stringstream" which is done // so we can hash multiple datatypes using only one function convert << m_key; std::string temp = convert.str(); for(unsigned x=0; x < temp.length(); ++x) { h = (h << 6) ^ (h >> 26) ^ temp[x]; } return abs(h % hashSize); } /* End of Hash */ template <class Key, class Value> void HashMap<Key, Value>::Insert(Key m_key, Value m_value) { if(IsFull()) { //std::cout<<"nINSERT ERROR - HASH MAP FULLn"; } else { int keyIndex = Hash(m_key); node* newNode = new node; // add new node newNode-> currentItem.key = m_key; newNode-> currentItem.value = m_value; newNode-> next = NULL; if(IsEmpty(keyIndex)) { head[keyIndex] = newNode; } else { node* temp = head[keyIndex]; while(temp-> next != NULL) { temp = temp-> next; } temp-> next = newNode; } ++bucketSize[keyIndex]; ++totElems; } }/* End of Insert */ template <class Key, class Value> bool HashMap<Key, Value>::Remove(Key m_key, Value deleteItem) { bool isFound = false; node* temp; int keyIndex = Hash(m_key); if(IsEmpty(keyIndex)) { //std::cout<<"nREMOVE ERROR - HASH MAP EMPTYn"; } else if(head[keyIndex]->currentItem.key == m_key && head[keyIndex]->currentItem.value == deleteItem) { temp = head[keyIndex]; head[keyIndex] = head[keyIndex]-> next; delete temp; --totElems; --bucketSize[keyIndex]; isFound = true; } else { for(temp = head[keyIndex];temp->next!=NULL;temp=temp->next) { if(temp->next->currentItem.key == m_key && temp->next->currentItem.value == deleteItem) { node* deleteNode = temp->next; temp-> next = temp-> next-> next; delete deleteNode; isFound = true; --totElems; --bucketSize[keyIndex]; break; } } } return isFound; }/* End of Remove */ template <class Key, class Value> void HashMap<Key, Value>::Sort(int keyIndex) { if(IsEmpty(keyIndex)) { //std::cout<<"nSORT ERROR - HASH MAP EMPTYn"; } else { int listSize = BucketSize(keyIndex); bool sorted = false; do{ sorted = true; int x = 0; for(node* temp = head[keyIndex]; temp->next!=NULL && x < listSize-1; temp=temp->next,++x) { if(temp-> currentItem.value > temp->next->currentItem.value) { std::swap(temp-> currentItem,temp->next->currentItem); sorted = false; } } --listSize; }while(!sorted); } }/* End of Sort */ template <class Key, class Value> int HashMap<Key, Value>::TableSize() { return hashSize; }/* End of TableSize */ template <class Key, class Value> int HashMap<Key, Value>::TotalElems() { return totElems; }/* End of TotalElems */ template <class Key, class Value> int HashMap<Key, Value>::BucketSize(int keyIndex) { return(!IsEmpty(keyIndex)) ? bucketSize[keyIndex]:0; }/* End of BucketSize */ template <class Key, class Value> int HashMap<Key, Value>::Count(Key m_key, Value searchItem) { int keyIndex = Hash(m_key); int search = 0; if(IsEmpty(keyIndex)) { //std::cout<<"nCOUNT ERROR - HASH MAP EMPTYn"; } else { for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next) { if(temp->currentItem.key == m_key && temp->currentItem.value == searchItem) { ++search; } } } return search; }/* End of Count */ template <class Key, class Value> int HashMap<Key, Value>::ContainsKey(Key m_key) { int keyIndex = Hash(m_key); int search = 0; if(IsEmpty(keyIndex)) { //std::cout<<"nCONTAINS KEY ERROR - HASH MAP EMPTYn"; } else { for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next) { if(temp->currentItem.key == m_key) { ++search; } } } return search; }/* End of ContainsKey */ template <class Key, class Value> void HashMap<Key, Value>::MakeEmpty() { totElems = 0; for(int x=0; x < hashSize; ++x) { if(!IsEmpty(x)) { //std::cout << "Destroying nodes ...n"; while(!IsEmpty(x)) { node* temp = head[x]; //std::cout << temp-> currentItem.value <<std::endl; head[x] = head[x]-> next; delete temp; } } bucketSize[x] = 0; } }/* End of MakeEmpty */ template <class Key, class Value> HashMap<Key, Value>::~HashMap() { MakeEmpty(); delete[] head; delete[] bucketSize; }/* End of ~HashMap */ // END OF THE HASH MAP CLASS // ----------------------------------------------------------- // START OF THE HASH MAP ITERATOR CLASS template <class Key, class Value> class HashMap<Key, Value>::Iterator : public std::iterator<std::forward_iterator_tag,Value>, public HashMap<Key, Value> { public: // Iterator constructor Iterator(node* otherIter = NULL) { itHead = otherIter; } ~Iterator() {} // The assignment and relational operators are straightforward Iterator& operator=(const Iterator& other) { itHead = other.itHead; return(*this); } bool operator==(const Iterator& other)const { return itHead == other.itHead; } bool operator!=(const Iterator& other)const { return itHead != other.itHead; } bool operator<(const Iterator& other)const { return itHead < other.itHead; } bool operator>(const Iterator& other)const { return other.itHead < itHead; } bool operator<=(const Iterator& other)const { return (!(other.itHead < itHead)); } bool operator>=(const Iterator& other)const { return (!(itHead < other.itHead)); } // Update my state such that I refer to the next element in the // HashMap. Iterator operator+(int incr) { node* temp = itHead; for(int x=0; x < incr && temp!= NULL; ++x) { temp = temp->next; } return temp; } Iterator operator+=(int incr) { for(int x=0; x < incr && itHead!= NULL; ++x) { itHead = itHead->next; } return itHead; } Iterator& operator++() // pre increment { if(itHead != NULL) { itHead = itHead->next; } return(*this); } Iterator operator++(int) // post increment { node* temp = itHead; this->operator++(); return temp; } KeyValue& operator[](int incr) { // Return "junk" data // to prevent the program from crashing if(itHead == NULL || (*this + incr) == NULL) { return junk; } return(*(*this + incr)); } // Return a reference to the value in the node. I do this instead // of returning by value so a caller can update the value in the // node directly. KeyValue& operator*() { // Return "junk" data // to prevent the program from crashing if(itHead == NULL) { return junk; } return itHead->currentItem; } KeyValue* operator->() { return(&**this); } private: node* itHead; KeyValue junk; }; #endif // http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489 // ============================================================================//     Author: K Perkins//     Date:   June 11, 2013//     Taken From: http://programmingnotes.org///     File:  HashMap.h//     Description: This is a class which implements various functions  //          demonstrating the use of a Hash Map. // ============================================================================#ifndef TEMPLATE_HASH_MAP#define TEMPLATE_HASH_MAP#include <iostream>#include <string>#include <sstream>#include <cstdlib> // if user doesnt define, this is the // default hash map sizeconst int HASH_SIZE = 350; template <class Key, class Value>class HashMap{public: HashMap(int hashSze = HASH_SIZE); /*   Function: Constructor initializes hash map Precondition: None Postcondition: Defines private variables */ bool IsEmpty(int keyIndex); /*   Function: Determines whether hash map is empty at the given hash                            map key index                           Precondition: Hash map has been created Postcondition: The function = true if the hash map is empty and the function = false if hash map is not empty */ bool  IsFull(); /*   Function: Determines whether hash map is full Precondition: Hash map has been created Postcondition: The function = true if the hash map is full and the function = false if hash map is not full */ int Hash(Key m_key); /*   Function: Computes and returns a hash map key index for a given item The returned key index is the given cell where the item resides Precondition:  Hash map has been created and is not full Postcondition: The hash key is returned */ void Insert(Key m_key, Value m_value); /*   Function: Adds new item to the back of the list at a given key in the hash map A unique hash key is automatically generated for each new item Precondition:  Hash map has been created and is not full Postcondition: Item is in the hash map */ bool Remove(Key m_key, Value deleteItem); /*   Function: Removes the first instance from the map whose value is "deleteItem" Precondition:  Hash map has been created and is not empty Postcondition: The function = true if deleteItem is found and the function = false if deleteItem is not found */ void Sort(int keyIndex); /*   Function: Sort the items in the map at the given hashmap key index Precondition: Hash map has been initialized Postcondition: The hash map is sorted */ int TableSize(); /*   Function: Return the size of the hash map Precondition: Hash map has been initialized Postcondition: The size of the hash map is returned */ int TotalElems(); /*   Function: Return the total number of elements contained in the hash map Precondition: Hash map has been initialized Postcondition: The size of the hash map is returned */ int BucketSize(int keyIndex); /*   Function: Return the number of items contained in the hash map cell at the given hashmap key index Precondition: Hash map has been initialized Postcondition: The size of the given key cell is returned */ int Count(Key m_key, Value searchItem); /*   Function: Return the number of times searchItem appears in the map at the given key Precondition: Hash map has been initialized Postcondition: The number of times searchItem appears in the map is returned */ int ContainsKey(Key m_key); /*   Function: Return the number of times the given key appears in the hashmap Precondition: Hash map has been initialized Postcondition: The number of times the given key appears in the map is returned */ void MakeEmpty(); /*   Function: Initializes hash map to an empty state Precondition: Hash map has been created Postcondition: Hash map no longer exists */ ~HashMap(); /*   Function: Removes the hash map Precondition: Hash map has been declared Postcondition: Hash map no longer exists */ //  -- ITERATOR CLASS -- class Iterator; /*   Function: Class declaration to the iterator Precondition: Hash map has been declared Postcondition: Hash Iterator has been declared */  Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;} /*   Function: Returns the beginning of the current hashmap key index Precondition: Hash map has been declared Postcondition: Hash cell has been returned to the Iterator */  Iterator end(int keyIndex=0){return NULL;} /*   Function: Returns the end of the current hashmap key index Precondition: Hash map has been declared Postcondition: Hash cell has been returned to the Iterator */ private: struct KeyValue  // struct to hold key/value pairs { Key key; Value value; }; struct node { KeyValue currentItem; node* next; }; node** head; // array of linked list declaration - front of each hash map cell int hashSize; // the size of the hash map (how many cells it has) int totElems; // holds the total number of elements in the entire table int* bucketSize; // holds the total number of elems in each specific hash map cell}; //=========================  Implementation  ================================// template <class Key, class Value>HashMap<Key, Value>::HashMap(int hashSze){ hashSize = hashSze; head = new node*[hashSize]; bucketSize = new int[hashSize]; for(int x=0; x < hashSize; ++x) { head[x] = NULL; bucketSize[x] = 0; } totElems = 0;}/* End of HashMap */ template <class Key, class Value>bool HashMap<Key, Value>::IsEmpty(int keyIndex){ if(keyIndex >=0 && keyIndex < hashSize) { return head[keyIndex] == NULL; } return true;}/* End of IsEmpty */ template <class Key, class Value>bool HashMap<Key, Value>::IsFull(){ try { node* location = new node; delete location; return false; } catch(std::bad_alloc&) { return true; }}/* End of IsFull */ template <class Key, class Value>int HashMap<Key, Value>::Hash(Key m_key){ long h = 19937; std::stringstream convert;  // convert the parameter to a string using "stringstream" which is done // so we can hash multiple datatypes using only one function convert << m_key; std::string temp = convert.str();  for(unsigned x=0; x < temp.length(); ++x) { h = (h << 6) ^ (h >> 26) ^ temp[x]; } return abs(h % hashSize);} /* End of Hash */ template <class Key, class Value>void HashMap<Key, Value>::Insert(Key m_key, Value m_value){ if(IsFull()) { //std::cout<<"nINSERT ERROR - HASH MAP FULLn"; } else { int keyIndex = Hash(m_key);                         node* newNode = new node;   // add new node newNode-> currentItem.key = m_key; newNode-> currentItem.value = m_value; newNode-> next = NULL; if(IsEmpty(keyIndex)) { head[keyIndex] = newNode; } else { node* temp = head[keyIndex]; while(temp-> next != NULL) { temp = temp-> next; } temp-> next = newNode; } ++bucketSize[keyIndex]; ++totElems;         }}/* End of Insert */ template <class Key, class Value>bool HashMap<Key, Value>::Remove(Key m_key, Value deleteItem) {    bool isFound = false;    node* temp;    int keyIndex = Hash(m_key);      if(IsEmpty(keyIndex))    {        //std::cout<<"nREMOVE ERROR - HASH MAP EMPTYn";    }    else if(head[keyIndex]->currentItem.key == m_key            && head[keyIndex]->currentItem.value == deleteItem)    {        temp = head[keyIndex];        head[keyIndex] = head[keyIndex]-> next;        delete temp;        --totElems;        --bucketSize[keyIndex];        isFound = true;    }    else    {                 for(temp = head[keyIndex];temp->next!=NULL;temp=temp->next)        {            if(temp->next->currentItem.key == m_key                && temp->next->currentItem.value == deleteItem)            {                node* deleteNode = temp->next;                temp-> next = temp-> next-> next;                delete deleteNode;                isFound = true;                --totElems;                --bucketSize[keyIndex];                break;            }        }            }    return isFound;}/* End of Remove */ template <class Key, class Value>void HashMap<Key, Value>::Sort(int keyIndex){             if(IsEmpty(keyIndex))    {        //std::cout<<"nSORT ERROR - HASH MAP EMPTYn";    }    else    {                 int listSize = BucketSize(keyIndex);        bool sorted = false;         do{            sorted = true;            int x = 0;            for(node* temp = head[keyIndex];                temp->next!=NULL && x < listSize-1;                temp=temp->next,++x)            {                if(temp-> currentItem.value > temp->next->currentItem.value)                {                    std::swap(temp-> currentItem,temp->next->currentItem);                    sorted = false;                }            }            --listSize;        }while(!sorted);    }}/* End of Sort */ template <class Key, class Value>int HashMap<Key, Value>::TableSize(){    return hashSize;}/* End of TableSize */ template <class Key, class Value>int HashMap<Key, Value>::TotalElems(){    return totElems;}/* End of TotalElems */ template <class Key, class Value>int HashMap<Key, Value>::BucketSize(int keyIndex){ return(!IsEmpty(keyIndex)) ? bucketSize[keyIndex]:0;}/* End of BucketSize */ template <class Key, class Value>int HashMap<Key, Value>::Count(Key m_key, Value searchItem) {    int keyIndex = Hash(m_key);    int search = 0;      if(IsEmpty(keyIndex))    {        //std::cout<<"nCOUNT ERROR - HASH MAP EMPTYn";    }    else    {                 for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)        {            if(temp->currentItem.key == m_key                && temp->currentItem.value == searchItem)            {                ++search;            }        }            }    return search;}/* End of Count */ template <class Key, class Value>int HashMap<Key, Value>::ContainsKey(Key m_key){    int keyIndex = Hash(m_key);    int search = 0;      if(IsEmpty(keyIndex))    {        //std::cout<<"nCONTAINS KEY ERROR - HASH MAP EMPTYn";    }    else    {                 for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)        {            if(temp->currentItem.key == m_key)            {                ++search;            }        }            }    return search;}/* End of ContainsKey */ template <class Key, class Value>void HashMap<Key, Value>::MakeEmpty(){    totElems = 0;    for(int x=0; x < hashSize; ++x)    {         if(!IsEmpty(x))        {            //std::cout << "Destroying nodes ...n";            while(!IsEmpty(x))            {                node* temp = head[x];                //std::cout << temp-> currentItem.value <<std::endl;                head[x] = head[x]-> next;                delete temp;            }         }        bucketSize[x] = 0;    }}/* End of MakeEmpty */ template <class Key, class Value>HashMap<Key, Value>::~HashMap() { MakeEmpty(); delete[] head; delete[] bucketSize;}/* End of ~HashMap */ //   END OF THE HASH MAP CLASS// -----------------------------------------------------------//   START OF THE HASH MAP ITERATOR CLASS template <class Key, class Value>class HashMap<Key, Value>::Iterator : public std::iterator<std::forward_iterator_tag,Value>, public HashMap<Key, Value> {public: // Iterator constructor Iterator(node* otherIter = NULL) { itHead = otherIter; } ~Iterator() {} // The assignment and relational operators are straightforward Iterator& operator=(const Iterator& other) { itHead = other.itHead; return(*this); } bool operator==(const Iterator& other)const { return itHead == other.itHead; } bool operator!=(const Iterator& other)const { return itHead != other.itHead; } bool operator<(const Iterator& other)const { return itHead < other.itHead; } bool operator>(const Iterator& other)const { return other.itHead < itHead; } bool operator<=(const Iterator& other)const { return (!(other.itHead < itHead)); } bool operator>=(const Iterator& other)const { return (!(itHead < other.itHead)); } // Update my state such that I refer to the next element in the // HashMap. Iterator operator+(int incr) { node* temp = itHead; for(int x=0; x < incr && temp!= NULL; ++x) { temp = temp->next; } return temp; } Iterator operator+=(int incr) { for(int x=0; x < incr && itHead!= NULL; ++x) { itHead = itHead->next; } return itHead; } Iterator& operator++() // pre increment { if(itHead != NULL) { itHead = itHead->next; } return(*this); } Iterator operator++(int) // post increment { node* temp = itHead; this->operator++(); return temp; } KeyValue& operator[](int incr) { // Return "junk" data // to prevent the program from crashing if(itHead == NULL || (*this + incr) == NULL) { return junk; } return(*(*this + incr)); } // Return a reference to the value in the node.  I do this instead // of returning by value so a caller can update the value in the // node directly. KeyValue& operator*() { // Return "junk" data // to prevent the program from crashing if(itHead == NULL) { return junk; } return itHead->currentItem; } KeyValue* operator->() { return(&**this); }private: node* itHead; KeyValue junk;}; #endif // http://programmingnotes.org/ ```

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The iterator class starts on line #381, and is built to support most of the standard relational operators, as well as arithmetic operators such as ‘+,+=,++’ (pre/post increment). The * (star), bracket [] and -> arrow operators are also supported. Click here for an overview demonstrating how custom iterators can be built.

The rest of the code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as many of its STL template class counterparts. Here are sample programs demonstrating its use.

``` #1 - Demonstrate Basic Use C++ // DEMONSTRATE BASIC USE AND THE REMOVE / SORT FUNCTIONS #include <iostream> #include <string> #include "HashMap.h" using namespace std; // iterator declaration typedef HashMap<string, int>::Iterator iterDec; int main() { // declare variables HashMap<string, int> hashMap; // place items into the hash map using the 'insert' function // NOTE: its OK for dupicate keys to be inserted into the hash map hashMap.Insert("BIOL", 585); hashMap.Insert("CPSC", 386); hashMap.Insert("ART", 101); hashMap.Insert("CPSC", 462); hashMap.Insert("HIST", 251); hashMap.Insert("CPSC", 301); hashMap.Insert("MATH", 270); hashMap.Insert("PE", 145); hashMap.Insert("BIOL", 134); hashMap.Insert("GEOL", 201); hashMap.Insert("CIS", 465); hashMap.Insert("CPSC", 240); hashMap.Insert("GEOL", 101); hashMap.Insert("MATH", 150); hashMap.Insert("DANCE", 134); hashMap.Insert("CPSC", 131); hashMap.Insert("ART", 345); hashMap.Insert("CHEM", 185); hashMap.Insert("PE", 125); hashMap.Insert("CPSC", 120); // display the number of times the key "CPSC" appears in the hashmap cout<<"The key 'CPSC' appears in the hash map "<< hashMap.ContainsKey("CPSC")<<" time(s)n"; // declare an iterator for the "CPSC" key so we can display data to screen iterDec it = hashMap.begin(hashMap.Hash("CPSC")); // display the first value cout<<"nThe first item with the key 'CPSC' is: " <<it[0].value<<endl; // display all the values in the hash map whose key matches "CPSC" // NOTE: its possible for multiple different keys types // to be placed into the same hash map bucket cout<<"nThese are all the items in the hash map whose key is 'CPSC': n"; for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x) { if(it[x].key == "CPSC") // make sure this is the key we are looking for { cout<<" Key-> "<<it[x].key<<"tValue-> "<<it[x].value<<endl; } } // remove the first value from the key "CPSC" cout<<"n[REMOVE THE VALUE '"<<it[0].value<<"' FROM THE KEY '"<<it[0].key<<"']n"; hashMap.Remove("CPSC",it[0].value); // display the number of times the key "CPSC" appears in the hashmap cout<<"nNow the key 'CPSC' only appears in the hash map "<< hashMap.ContainsKey("CPSC")<<" time(s)n"; // update the iterator to the current hash map state it = hashMap.begin(hashMap.Hash("CPSC")); // sort the values in the hash map bucket whose key is "CSPC" hashMap.Sort(hashMap.Hash("CPSC")); // display the values whose key matches "CPSC" cout<<"nThese are the sorted items in the hash map whose key is 'CPSC': n"; for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x) { if(it[x].key == "CPSC") { cout<<" Key-> "<<it[x].key<<"tValue-> "<<it[x].value<<endl; } } // display all the key/values in the entire hash map cout<<"nThese are all of the items in the entire hash map: n"; for(int x=0; x < hashMap.TableSize(); ++x) { if(!hashMap.IsEmpty(x)) { for(iterDec iter = hashMap.begin(x); iter != hashMap.end(x); ++iter) { cout<<" Key-> "<<(*iter).key<<"tValue-> "<<iter->value<<endl; } cout<<endl; } } // display the total number of items in the hash map cout<<"The total number of items in the hash map is: "<< hashMap.TotalElems()<<endl; return 0; }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104 // DEMONSTRATE BASIC USE AND THE REMOVE / SORT FUNCTIONS#include <iostream>#include <string>#include "HashMap.h"using namespace std; // iterator declarationtypedef HashMap<string, int>::Iterator iterDec; int main(){    // declare variables    HashMap<string, int> hashMap;        // place items into the hash map using the 'insert' function    // NOTE: its OK for dupicate keys to be inserted into the hash map    hashMap.Insert("BIOL", 585);    hashMap.Insert("CPSC", 386);    hashMap.Insert("ART", 101);    hashMap.Insert("CPSC", 462);    hashMap.Insert("HIST", 251);    hashMap.Insert("CPSC", 301);    hashMap.Insert("MATH", 270);    hashMap.Insert("PE", 145);    hashMap.Insert("BIOL", 134);    hashMap.Insert("GEOL", 201);    hashMap.Insert("CIS", 465);    hashMap.Insert("CPSC", 240);    hashMap.Insert("GEOL", 101);    hashMap.Insert("MATH", 150);    hashMap.Insert("DANCE", 134);    hashMap.Insert("CPSC", 131);    hashMap.Insert("ART", 345);    hashMap.Insert("CHEM", 185);    hashMap.Insert("PE", 125);    hashMap.Insert("CPSC", 120);        // display the number of times the key "CPSC" appears in the hashmap    cout<<"The key 'CPSC' appears in the hash map "<<        hashMap.ContainsKey("CPSC")<<" time(s)n";        // declare an iterator for the "CPSC" key so we can display data to screen    iterDec it = hashMap.begin(hashMap.Hash("CPSC"));        // display the first value    cout<<"nThe first item with the key 'CPSC' is: "        <<it[0].value<<endl;        // display all the values in the hash map whose key matches "CPSC"    // NOTE: its possible for multiple different keys types    //   to be placed into the same hash map bucket        cout<<"nThese are all the items in the hash map whose key is 'CPSC': n";    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)    {        if(it[x].key == "CPSC") // make sure this is the key we are looking for        {            cout<<"  Key-> "<<it[x].key<<"tValue-> "<<it[x].value<<endl;        }    }        // remove the first value from the key "CPSC"    cout<<"n[REMOVE THE VALUE '"<<it[0].value<<"' FROM THE KEY '"<<it[0].key<<"']n";        hashMap.Remove("CPSC",it[0].value);        // display the number of times the key "CPSC" appears in the hashmap    cout<<"nNow the key 'CPSC' only appears in the hash map "<<        hashMap.ContainsKey("CPSC")<<" time(s)n";             // update the iterator to the current hash map state    it = hashMap.begin(hashMap.Hash("CPSC"));        // sort the values in the hash map bucket whose key is "CSPC"    hashMap.Sort(hashMap.Hash("CPSC"));        // display the values whose key matches "CPSC"    cout<<"nThese are the sorted items in the hash map whose key is 'CPSC': n";    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)    {        if(it[x].key == "CPSC")        {            cout<<"  Key-> "<<it[x].key<<"tValue-> "<<it[x].value<<endl;        }    }                    // display all the key/values in the entire hash map     cout<<"nThese are all of the items in the entire hash map: n";    for(int x=0; x < hashMap.TableSize(); ++x)    {        if(!hashMap.IsEmpty(x))        {            for(iterDec iter = hashMap.begin(x); iter != hashMap.end(x); ++iter)            {                cout<<"  Key-> "<<(*iter).key<<"tValue-> "<<iter->value<<endl;            }            cout<<endl;        }            }        // display the total number of items in the hash map    cout<<"The total number of items in the hash map is: "<<        hashMap.TotalElems()<<endl;                   return 0;}// http://programmingnotes.org/ ```

SAMPLE OUTPUT:

`The key 'CPSC' appears in the hash map 6 time(s)`

``` The first item with the key 'CPSC' is: 386 These are all the items in the hash map whose key is 'CPSC': Key-> CPSC Value-> 386 Key-> CPSC Value-> 462 Key-> CPSC Value-> 301 Key-> CPSC Value-> 240 Key-> CPSC Value-> 131 Key-> CPSC Value-> 120 [REMOVE THE VALUE '386' FROM THE KEY 'CPSC'] Now the key 'CPSC' only appears in the hash map 5 time(s) These are the sorted items in the hash map whose key is 'CPSC': Key-> CPSC Value-> 120 Key-> CPSC Value-> 131 Key-> CPSC Value-> 240 Key-> CPSC Value-> 301 Key-> CPSC Value-> 462 These are all of the items in the entire hash map: Key-> CIS Value-> 465 Key-> DANCE Value-> 134 Key-> PE Value-> 145 Key-> PE Value-> 125 Key-> MATH Value-> 270 Key-> MATH Value-> 150 Key-> GEOL Value-> 201 Key-> GEOL Value-> 101 Key-> CPSC Value-> 120 Key-> CPSC Value-> 131 Key-> CPSC Value-> 240 Key-> CPSC Value-> 301 Key-> CPSC Value-> 462 Key-> BIOL Value-> 585 Key-> BIOL Value-> 134 Key-> ART Value-> 101 Key-> ART Value-> 345 Key-> CHEM Value-> 185 Key-> HIST Value-> 251 ```

```The total number of items in the hash map is: 19 ```

``` #2 - Display Items In A Struct C++ // DISPLAY ALL DATA INSIDE HASH MAP USING STD::STRING / INT / DOUBLE / STRUCT #include <iostream> #include <string> #include "HashMap.h" using namespace std; // sample struct demo struct MyStruct { string car; int year; double mpg; // struct comparison operators // used for 'remove' function bool operator == (const MyStruct& rhs)const { return car == rhs.car && year == rhs.year && mpg == rhs.mpg; } // used for 'sort' function bool operator > (const MyStruct& rhs)const { return car > rhs.car; } };// end of MyStruct // iterator declaration typedef HashMap<string, MyStruct>::Iterator iterDec; int main() { // declare variables MyStruct access; HashMap<string, MyStruct> hashMap(10); // --- initialize data for car #1 --- access.car = "Ford Fusion"; access.year = 2006; access.mpg = 28.5; hashMap.Insert("Kenneth",access); // --- initialize data for car #2 --- access.car = "BMW 535i"; access.year = 2014; access.mpg = 25.4; hashMap.Insert("Kenneth",access); // --- initialize data for car #3 --- access.car = "Nissan Altima"; access.year = 2011; access.mpg = 30.7; hashMap.Insert("Jessica",access); // --- initialize data for car #4 --- access.car = "Acura Integra"; access.year = 2001; access.mpg = 20.2; hashMap.Insert("Kenneth",access); // diplay how many cars "Kenneth" owns cout <<"'Kenneth' owns "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl; // display all items in the hash map // NOTE: its possible for multiple different keys types // to be placed into the same hash map bucket cout<<"nThese are all of the cars in the hash map: n"; for(int x=0; x < hashMap.TableSize(); ++x) { if(!hashMap.IsEmpty(x)) { // initialize an iterator iterDec iter = hashMap.begin(x); // display the key cout<<(*iter).key<<"'s car(s)n"; // display all the values for(;iter != hashMap.end(x); ++iter) { cout<<"tCar: "<<iter->value.car <<"ntYear: "<<iter->value.year <<"ntMPG: "<<iter->value.mpg<<endl<<endl; } } } // display the number of items in the hash map cout<<"The total number of cars in the hash map is: "<< hashMap.TotalElems()<<endl; // sort the cars that "Kenneth" owns by name cout<<"nSorting the cars that 'Kenneth' owns by name.. n"; hashMap.Sort(hashMap.Hash("Kenneth")); // display all items in the hash map again cout<<"nAgain, these are all of the cars in the hash map: n"; for(int x=0; x < hashMap.TableSize(); ++x) { if(!hashMap.IsEmpty(x)) { // initialize an iterator iterDec iter = hashMap.begin(x); // display the key cout<<iter->key<<"'s car(s)n"; // display all the values for(;iter != hashMap.end(x); ++iter) { cout<<"tCar: "<<(*iter).value.car <<"ntYear: "<<(*iter).value.year <<"ntMPG: "<<(*iter).value.mpg<<endl<<endl; } } } // remove the car 'Acura Integra' from "Kenneth's" inventory for(iterDec iter = hashMap.begin(hashMap.Hash("Kenneth")); iter != hashMap.end(hashMap.Hash("Kenneth")); ++iter) { if(iter->value.car == "Acura Integra") { cout<<"'"<<iter->value.car<<"' has been removed from 'Kenneth's' inventory..n"; hashMap.Remove("Kenneth",(*iter).value); break; } } // display how many cars "Kenneth" owns cout <<"n'Kenneth' now owns only "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl; // display all items in the hash map one more time cout<<"nThese are all of the cars in the hash map with the 'Acura Integra' removed: n"; for(int x=0; x < hashMap.TableSize(); ++x) { if(!hashMap.IsEmpty(x)) { // initialize an iterator iterDec iter = hashMap.begin(x); // display the key cout<<(*iter).key<<"'s car(s)n"; // display all the values for(;iter != hashMap.end(x); ++iter) { cout<<"tCar: "<<iter->value.car <<"ntYear: "<<iter->value.year <<"ntMPG: "<<iter->value.mpg<<endl<<endl; } } } // display the number of items in the hash map cout<<"The total number of cars in the hash map is: "<< hashMap.TotalElems()<<endl; return 0; }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159 // DISPLAY ALL DATA INSIDE HASH MAP USING STD::STRING / INT / DOUBLE / STRUCT#include <iostream>#include <string>#include "HashMap.h"using namespace std; // sample struct demostruct MyStruct{    string car;    int year;    double mpg;        // struct comparison operators    // used for 'remove' function    bool operator == (const MyStruct& rhs)const    {        return car == rhs.car &&            year == rhs.year &&            mpg == rhs.mpg;    }        // used for 'sort' function    bool operator > (const MyStruct& rhs)const    {        return car > rhs.car;    }    };// end of MyStruct // iterator declarationtypedef HashMap<string, MyStruct>::Iterator iterDec; int main(){    // declare variables    MyStruct access;     HashMap<string, MyStruct> hashMap(10);        // --- initialize data for car #1 ---    access.car = "Ford Fusion";    access.year = 2006;    access.mpg = 28.5;            hashMap.Insert("Kenneth",access);                    // --- initialize data for car #2 ---    access.car = "BMW 535i";    access.year = 2014;    access.mpg = 25.4;    hashMap.Insert("Kenneth",access);        // --- initialize data for car #3 ---    access.car = "Nissan Altima";    access.year = 2011;    access.mpg = 30.7;    hashMap.Insert("Jessica",access);             // --- initialize data for car #4 ---    access.car = "Acura Integra";    access.year = 2001;    access.mpg = 20.2;        hashMap.Insert("Kenneth",access);                   // diplay how many cars "Kenneth" owns    cout <<"'Kenneth' owns "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;                     // display all items in the hash map    // NOTE: its possible for multiple different keys types    //   to be placed into the same hash map bucket         cout<<"nThese are all of the cars in the hash map: n";    for(int x=0; x < hashMap.TableSize(); ++x)    {        if(!hashMap.IsEmpty(x))        {            // initialize an iterator            iterDec iter = hashMap.begin(x);                        // display the key            cout<<(*iter).key<<"'s car(s)n";            // display all the values             for(;iter != hashMap.end(x); ++iter)            {                cout<<"tCar: "<<iter->value.car                    <<"ntYear: "<<iter->value.year                    <<"ntMPG: "<<iter->value.mpg<<endl<<endl;                                            }        }            }                       // display the number of items in the hash map    cout<<"The total number of cars in the hash map is: "<<        hashMap.TotalElems()<<endl;           // sort the cars that "Kenneth" owns by name    cout<<"nSorting the cars that 'Kenneth' owns by name.. n";             hashMap.Sort(hashMap.Hash("Kenneth"));            // display all items in the hash map again      cout<<"nAgain, these are all of the cars in the hash map: n";    for(int x=0; x < hashMap.TableSize(); ++x)    {        if(!hashMap.IsEmpty(x))        {            // initialize an iterator            iterDec iter = hashMap.begin(x);                        // display the key            cout<<iter->key<<"'s car(s)n";            // display all the values             for(;iter != hashMap.end(x); ++iter)            {                cout<<"tCar: "<<(*iter).value.car                    <<"ntYear: "<<(*iter).value.year                    <<"ntMPG: "<<(*iter).value.mpg<<endl<<endl;                            }        }            }      // remove the car 'Acura Integra' from "Kenneth's" inventory    for(iterDec iter = hashMap.begin(hashMap.Hash("Kenneth"));         iter != hashMap.end(hashMap.Hash("Kenneth")); ++iter)    {         if(iter->value.car == "Acura Integra")        {            cout<<"'"<<iter->value.car<<"' has been removed from 'Kenneth's' inventory..n";            hashMap.Remove("Kenneth",(*iter).value);            break;        }    }            // display how many cars "Kenneth" owns    cout <<"n'Kenneth' now owns only "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;                         // display all items in the hash map one more time      cout<<"nThese are all of the cars in the hash map with the 'Acura Integra' removed: n";    for(int x=0; x < hashMap.TableSize(); ++x)    {        if(!hashMap.IsEmpty(x))        {            // initialize an iterator            iterDec iter = hashMap.begin(x);                        // display the key            cout<<(*iter).key<<"'s car(s)n";            // display all the values             for(;iter != hashMap.end(x); ++iter)            {                cout<<"tCar: "<<iter->value.car                    <<"ntYear: "<<iter->value.year                    <<"ntMPG: "<<iter->value.mpg<<endl<<endl;            }        }            }             // display the number of items in the hash map    cout<<"The total number of cars in the hash map is: "<<        hashMap.TotalElems()<<endl;                       return 0;}// http://programmingnotes.org/ ```

SAMPLE OUTPUT:

`'Kenneth' owns 3 cars`

``` These are all of the cars in the hash map: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: Ford Fusion Year: 2006 MPG: 28.5 Car: BMW 535i Year: 2014 MPG: 25.4 Car: Acura Integra Year: 2001 MPG: 20.2 ----------------------------------------------------- The total number of cars in the hash map is: 4 Sorting the cars that 'Kenneth' owns by name.. Again, these are all of the cars in the hash map: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: Acura Integra Year: 2001 MPG: 20.2 Car: BMW 535i Year: 2014 MPG: 25.4 Car: Ford Fusion Year: 2006 MPG: 28.5 ----------------------------------------------------- 'Acura Integra' has been removed from 'Kenneth's' inventory.. 'Kenneth' now owns only 2 cars These are all of the cars in the hash map with the 'Acura Integra' removed: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: BMW 535i Year: 2014 MPG: 25.4 Car: Ford Fusion Year: 2006 MPG: 28.5 ----------------------------------------------------- ```

```The total number of cars in the hash map is: 3 ```

## C++ || Snippet – How To Convert A Decimal Number Into Binary

This page will demonstrate how to convert a decimal number (i.e a whole number) into its binary equivalent. So for example, if the decimal number of 26 was entered into the program, it would display the converted binary value of 11010.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

```How To Count In Binary The "Long" Datatype - What Is It? While Loops Online Binary to Decimal Converter - Verify For Correct Results How To Reverse A String ```

If you are looking for sample code which converts binary to decimal, check back here soon!

``` Convert A Decimal Number Into Binary C++ #include <iostream> #include <string> #include <algorithm> using namespace std; // function prototype string DecToBin(long long decNum); int main() { // declare variables long long decNum = 0; string binaryNum=""; // use a string instead of an int to avoid // overflow, because binary numbers can grow large quick cout<<"Please enter an integer value: "; cin >> decNum; if(decNum < 0) { binaryNum = "-"; } // call function to convert decimal to binary binaryNum += DecToBin(decNum); // display data to user cout<<"nThe integer value of "<<decNum<<" = "<<binaryNum<<" in binary"<<endl; return 0; } string DecToBin(long long decNum) { string binary = ""; // use this string to save the binary number if(decNum < 0) // if input is a neg number, make it positive { decNum *= -1; } // converts decimal to binary using division and modulus while(decNum > 0) { binary += (decNum % 2)+'0'; // convert int to char decNum /= 2; } // reverse the string reverse(binary.begin(), binary.end()); return binary; }// http://programmingnotes.org/ 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253 #include <iostream>#include <string>#include <algorithm> using namespace std; // function prototypestring DecToBin(long long decNum); int main(){ // declare variables long long decNum = 0; string binaryNum=""; // use a string instead of an int to avoid   // overflow, because binary numbers can grow large quick  cout<<"Please enter an integer value: "; cin >> decNum;  if(decNum < 0) { binaryNum = "-"; }  // call function to convert decimal to binary binaryNum += DecToBin(decNum);  // display data to user cout<<"nThe integer value of "<<decNum<<" = "<<binaryNum<<" in binary"<<endl;  return 0;} string DecToBin(long long decNum){ string binary = ""; // use this string to save the binary number  if(decNum < 0) // if input is a neg number, make it positive {               decNum *= -1; }                     // converts decimal to binary using division and modulus while(decNum > 0) { binary += (decNum % 2)+'0'; // convert int to char decNum /= 2; }  // reverse the string reverse(binary.begin(), binary.end());  return binary;}// http://programmingnotes.org/ ```

The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output
Note: The code was compiled 3 separate times to display different output

`====== RUN 1 ======`

``` Please enter an integer value: 1987 The integer value of 1987 = 11111000011 in binary ====== RUN 2 ====== Please enter an integer value: -26 The integer value of -26 = -11010 in binary ====== RUN 3 ====== Please enter an integer value: 12345678910 ```

```The integer value of 12345678910 = 1011011111110111000001110000111110 in binary ```

## C++ || Custom Template Hash Table With Iterator Using Separate Chaining

Looking for sample code for a Hash Map? Click here!

Before we get into the code, what is a Hash Table? Simply put, a Hash Table is a data structure used to implement an associative array; one that can map unique “keys” to specific values. While a standard array requires that indice subscripts be integers, a hash table can use a floating point value, a string, another array, or even a structure as the index. That index is called the “key,” and the contents within the array at that specific index location is called the value. A hash table uses a hash function to generate an index into the table, creating buckets or slots, from which the correct value can be found.

To illustrate, compare a standard array full of data (100 elements). If the position was known for the specific item that we wanted to access within the array, we could quickly access it. For example, if we wanted to access the data located at index #5 in the array, we could access it by doing:

``` array[5]; // do something with the data ```

Here, we dont have to search through each element in the array to find what we need, we just access it at index #5. The question is, how do we know that index #5 stores the data that we are looking for? If we have a large set of data, doing a sequential search over each item within the array can be very inefficient. That is where hashing comes in handy. Given a “key,” we can apply a hash function to a unique index or bucket to find the data that we wish to access.

So in essence, a hash table is a data structure that stores key/value pairs, and is typically used because they are ideal for doing a quick search of items.

Though hashing is ideal, it isnt perfect. It is possible for multiple items to be hashed into the same location. Hash “collisions” are practically unavoidable when hashing large data sets. The code demonstrated on this page handles collisions via separate chaining, utilizing an array of linked list head nodes to store multiple values within one bucket – should any collisions occur.

An iterator was also implemented, making data access that much more simple within the hash table class. Click here for an overview demonstrating how custom iterators can be built.

Looking for sample code for a Hash Map? Click here!

=== CUSTOM TEMPLATE HASH TABLE WITH ITERATOR ===

``` #include 'HashTable.h' - Hash Table With Iterator C++ // ============================================================================ // Author: K Perkins // Date: Jan 18, 2013 // Taken From: http://programmingnotes.org/ // File: HashTable.h // Description: This is a class which implements various functions which // demonstrates the use of a Hash Table. // ============================================================================ #ifndef TEMPLATE_HASH_TABLE #define TEMPLATE_HASH_TABLE #include <iostream> #include <string> #include <sstream> #include <cstdlib> // if user doesnt define, this is the // default hash table size const int HASH_SIZE = 100; template <class ItemType> class HashTable { public: HashTable(int hashSze = HASH_SIZE); /* Function: Constructor initializes hash table Precondition: None Postcondition: Defines private variables */ bool IsEmpty(int key); /* Function: Determines whether hash table is empty at the given key Precondition: Hash table has been created Postcondition: The function = true if the hash table is empty and the function = false if hash table is not empty */ bool IsFull(); /* Function: Determines whether hash table is full Precondition: Hash table has been created Postcondition: The function = true if the hash table is full and the function = false if hash table is not full */ int Hash(ItemType newItem); /* Function: Computes and returns a unique hash key for a given item The returned key is the given cell where the item resides Precondition: Hash table has been created and is not full Postcondition: The hash key is returned */ void Insert(ItemType newItem); /* Function: Adds newItem to the back of the list at a given key in the hash table A unique hash key is automatically generated for each newItem Precondition: Hash table has been created and is not full Postcondition: Item is in the hash table */ void Append(int key, ItemType newItem); /* Function: Adds new item to the end of the list at a given key in the hash table Precondition: Hash table has been created and is not full Postcondition: Item is in the hash table */ bool Remove(ItemType deleteItem, int key = -1); /* Function: Removes the first instance from the table whose value is "deleteItem" Optional second parameter indicates the key where deleteItem is located Precondition: Hash table has been created and is not empty Postcondition: The function = true if deleteItem is found and the function = false if deleteItem is not found */ void Sort(int key); /* Function: Sort the items in the table at the given key Precondition: Hash table has been initialized Postcondition: The hash table is sorted */ int TableSize(); /* Function: Return the size of the hash table Precondition: Hash table has been initialized Postcondition: The size of the hash table is returned */ int TotalElems(); /* Function: Return the total number of elements contained in the hash table Precondition: Hash table has been initialized Postcondition: The size of the hash table is returned */ int BucketSize(int key); /* Function: Return the number of items contained in the hash table cell at the given key Precondition: Hash table has been initialized Postcondition: The size of the given key cell is returned */ int Count(ItemType searchItem); /* Function: Return the number of times searchItem appears in the table. Only works on items located in their correctly hashed cells Precondition: Hash table has been initialized Postcondition: The number of times searchItem appears in the table is returned */ void MakeEmpty(); /* Function: Initializes hash table to an empty state Precondition: Hash table has been created Postcondition: Hash table no longer exists */ ~HashTable(); /* Function: Removes the hash table Precondition: Hash table has been declared Postcondition: Hash table no longer exists */ // -- ITERATOR CLASS -- class Iterator; /* Function: Class declaration to the iterator Precondition: Hash table has been declared Postcondition: Hash Iterator has been declared */ Iterator begin(int key){return(!IsEmpty(key)) ? head[key]:NULL;} /* Function: Returns the beginning of the current hash cell list Precondition: Hash table has been declared Postcondition: Hash cell has been returned to the Iterator */ Iterator end(int key=0){return NULL;} /* Function: Returns the end of the current hash cell list Precondition: Hash table has been declared Postcondition: Hash cell has been returned to the Iterator */ private: struct node { ItemType currentItem; node* next; }; node** head; // array of linked list declaration - front of each hash table cell int hashSize; // the size of the hash table (how many cells it has) int totElems; // holds the total number of elements in the entire table int* bucketSize; // holds the total number of elems in each specific hash table cell }; //========================= Implementation ================================// template<class ItemType> HashTable<ItemType>::HashTable(int hashSze) { hashSize = hashSze; head = new node*[hashSize]; bucketSize = new int[hashSize]; for(int x=0; x < hashSize; ++x) { head[x] = NULL; bucketSize[x] = 0; } totElems = 0; }/* End of HashTable */ template<class ItemType> bool HashTable<ItemType>::IsEmpty(int key) { if(key >=0 && key < hashSize) { return head[key] == NULL; } return true; }/* End of IsEmpty */ template<class ItemType> bool HashTable<ItemType>::IsFull() { try { node* location = new node; delete location; return false; } catch(std::bad_alloc&) { return true; } }/* End of IsFull */ template<class ItemType> int HashTable<ItemType>::Hash(ItemType newItem) { long h = 19937; std::stringstream convert; // convert the parameter to a string using "stringstream" which is done // so we can hash multiple datatypes using only one function convert << newItem; std::string temp = convert.str(); for(unsigned x=0; x < temp.length(); ++x) { h = (h << 6) ^ (h >> 26) ^ temp[x]; } return abs(h % hashSize); } /* End of Hash */ template<class ItemType> void HashTable<ItemType>::Insert(ItemType newItem) { if(IsFull()) { //std::cout<<"nINSERT ERROR - HASH TABLE FULLn"; } else { int key = Hash(newItem); Append(key,newItem); } }/* End of Insert */ template<class ItemType> void HashTable<ItemType>::Append(int key, ItemType newItem) { if(IsFull()) { //std::cout<<"nAPPEND ERROR - HASH TABLE FULLn"; } else { node* newNode = new node; // adds new node newNode-> currentItem = newItem; newNode-> next = NULL; if(IsEmpty(key)) { head[key] = newNode; } else { node* tempPtr = head[key]; while(tempPtr-> next != NULL) { tempPtr = tempPtr-> next; } tempPtr-> next = newNode; } ++bucketSize[key]; ++totElems; } }/* End of Append */ template<class ItemType> bool HashTable<ItemType>::Remove(ItemType deleteItem, int key) { bool isFound = false; node* tempPtr; if(key == -1) { key = Hash(deleteItem); } if(IsEmpty(key)) { //std::cout<<"nREMOVE ERROR - HASH TABLE EMPTYn"; } else if(head[key]->currentItem == deleteItem) { tempPtr = head[key]; head[key] = head[key]-> next; delete tempPtr; --totElems; --bucketSize[key]; isFound = true; } else { for(tempPtr = head[key];tempPtr->next!=NULL;tempPtr=tempPtr->next) { if(tempPtr->next->currentItem == deleteItem) { node* deleteNode = tempPtr->next; tempPtr-> next = tempPtr-> next-> next; delete deleteNode; isFound = true; --totElems; --bucketSize[key]; break; } } } return isFound; }/* End of Remove */ template<class ItemType> void HashTable<ItemType>::Sort(int key) { if(IsEmpty(key)) { //std::cout<<"nSORT ERROR - HASH TABLE EMPTYn"; } else { int listSize = BucketSize(key); bool sorted = false; do{ sorted = true; int x = 0; for(node* tempPtr = head[key]; tempPtr->next!=NULL && x < listSize-1; tempPtr=tempPtr->next,++x) { if(tempPtr-> currentItem > tempPtr->next->currentItem) { ItemType temp = tempPtr-> currentItem; tempPtr-> currentItem = tempPtr->next->currentItem; tempPtr->next->currentItem = temp; sorted = false; } } --listSize; }while(!sorted); } }/* End of Sort */ template<class ItemType> int HashTable<ItemType>::TableSize() { return hashSize; }/* End of TableSize */ template<class ItemType> int HashTable<ItemType>::TotalElems() { return totElems; }/* End of TotalElems */ template<class ItemType> int HashTable<ItemType>::BucketSize(int key) { return(!IsEmpty(key)) ? bucketSize[key]:0; }/* End of BucketSize */ template<class ItemType> int HashTable<ItemType>::Count(ItemType searchItem) { int key = Hash(searchItem); int search = 0; if(IsEmpty(key)) { //std::cout<<"nCOUNT ERROR - HASH TABLE EMPTYn"; } else { for(node* tempPtr = head[key];tempPtr!=NULL;tempPtr=tempPtr->next) { if(tempPtr->currentItem == searchItem) { ++search; } } } return search; }/* End of Count */ template<class ItemType> void HashTable<ItemType>::MakeEmpty() { totElems = 0; for(int x=0; x < hashSize; ++x) { if(!IsEmpty(x)) { //std::cout << "Destroying nodes ...n"; while(!IsEmpty(x)) { node* temp = head[x]; //std::cout << temp-> currentItem <<std::endl; head[x] = head[x]-> next; delete temp; } } bucketSize[x] = 0; } }/* End of MakeEmpty */ template<class ItemType> HashTable<ItemType>::~HashTable() { MakeEmpty(); delete[] head; delete[] bucketSize; }/* End of ~HashTable */ // END OF THE HASH TABLE CLASS // ----------------------------------------------------------- // START OF THE HASH TABLE ITERATOR CLASS template <class ItemType> class HashTable<ItemType>::Iterator : public std::iterator<std::forward_iterator_tag,ItemType>, public HashTable<ItemType> { public: // Iterator constructor Iterator(node* otherIter = NULL) { itHead = otherIter; } ~Iterator() {} // The assignment and relational operators are straightforward Iterator& operator=(const Iterator& other) { itHead = other.itHead; return(*this); } bool operator==(const Iterator& other)const { return itHead == other.itHead; } bool operator!=(const Iterator& other)const { return itHead != other.itHead; } bool operator<(const Iterator& other)const { return itHead < other.itHead; } bool operator>(const Iterator& other)const { return other.itHead < itHead; } bool operator<=(const Iterator& other)const { return (!(other.itHead < itHead)); } bool operator>=(const Iterator& other)const { return (!(itHead < other.itHead)); } // Update my state such that I refer to the next element in the // HashTable. Iterator operator+(int incr) { node* temp = itHead; for(int x=0; x < incr && temp!= NULL; ++x) { temp = temp->next; } return temp; } Iterator operator+=(int incr) { for(int x=0; x < incr && itHead!= NULL; ++x) { itHead = itHead->next; } return itHead; } Iterator& operator++() // pre increment { if(itHead != NULL) { itHead = itHead->next; } return(*this); } Iterator operator++(int) // post increment { node* temp = itHead; this->operator++(); return temp; } ItemType& operator[](int incr) { // Return "junk" data // to prevent the program from crashing if(itHead == NULL || (*this + incr) == NULL) { return junk; } return(*(*this + incr)); } // Return a reference to the value in the node. I do this instead // of returning by value so a caller can update the value in the // node directly. ItemType& operator*() { // Return "junk" data // to prevent the program from crashing if(itHead == NULL) { return junk; } return itHead->currentItem; } ItemType* operator->() { return(&**this); } private: node* itHead; ItemType junk; }; #endif // http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476 // ============================================================================//     Author: K Perkins//     Date:   Jan 18, 2013//     Taken From: http://programmingnotes.org///     File:  HashTable.h//     Description: This is a class which implements various functions which //          demonstrates the use of a Hash Table. // ============================================================================#ifndef TEMPLATE_HASH_TABLE#define TEMPLATE_HASH_TABLE#include <iostream>#include <string>#include <sstream>#include <cstdlib> // if user doesnt define, this is the // default hash table sizeconst int HASH_SIZE = 100; template <class ItemType>class HashTable{public: HashTable(int hashSze = HASH_SIZE); /*   Function: Constructor initializes hash table Precondition: None Postcondition: Defines private variables */ bool IsEmpty(int key); /*   Function: Determines whether hash table is empty at the given key Precondition: Hash table has been created Postcondition: The function = true if the hash table is empty and the function = false if hash table is not empty */ bool  IsFull(); /*   Function: Determines whether hash table is full Precondition: Hash table has been created Postcondition: The function = true if the hash table is full and the function = false if hash table is not full */ int Hash(ItemType newItem); /*   Function: Computes and returns a unique hash key for a given item The returned key is the given cell where the item resides Precondition:  Hash table has been created and is not full Postcondition: The hash key is returned */ void Insert(ItemType newItem); /*   Function: Adds newItem to the back of the list at a given key in the hash table A unique hash key is automatically generated for each newItem Precondition:  Hash table has been created and is not full Postcondition: Item is in the hash table */ void Append(int key, ItemType newItem); /*   Function: Adds new item to the end of the list at a given key in the hash table Precondition:  Hash table has been created and is not full Postcondition: Item is in the hash table */ bool Remove(ItemType deleteItem, int key = -1); /*   Function: Removes the first instance from the table whose value is "deleteItem"   Optional second parameter indicates the key where deleteItem is located Precondition:  Hash table has been created and is not empty Postcondition: The function = true if deleteItem is found and the function = false if deleteItem is not found */ void Sort(int key); /*   Function: Sort the items in the table at the given key Precondition: Hash table has been initialized Postcondition: The hash table is sorted */ int TableSize(); /*   Function: Return the size of the hash table Precondition: Hash table has been initialized Postcondition: The size of the hash table is returned */ int TotalElems(); /*   Function: Return the total number of elements contained in the hash table Precondition: Hash table has been initialized Postcondition: The size of the hash table is returned */ int BucketSize(int key); /*   Function: Return the number of items contained in the hash table cell at the given key Precondition: Hash table has been initialized Postcondition: The size of the given key cell is returned */ int Count(ItemType searchItem); /*   Function: Return the number of times searchItem appears in the table. Only works on items located in their correctly hashed cells Precondition: Hash table has been initialized Postcondition: The number of times searchItem appears in the table is returned */ void MakeEmpty(); /*   Function: Initializes hash table to an empty state Precondition: Hash table has been created Postcondition: Hash table no longer exists */ ~HashTable(); /*   Function: Removes the hash table Precondition: Hash table has been declared Postcondition: Hash table no longer exists */ //  -- ITERATOR CLASS -- class Iterator; /*   Function: Class declaration to the iterator Precondition: Hash table has been declared Postcondition: Hash Iterator has been declared */  Iterator begin(int key){return(!IsEmpty(key)) ? head[key]:NULL;} /*   Function: Returns the beginning of the current hash cell list Precondition: Hash table has been declared Postcondition: Hash cell has been returned to the Iterator */  Iterator end(int key=0){return NULL;} /*   Function: Returns the end of the current hash cell list Precondition: Hash table has been declared Postcondition: Hash cell has been returned to the Iterator */ private: struct node { ItemType currentItem; node* next; }; node** head; // array of linked list declaration - front of each hash table cell int hashSize; // the size of the hash table (how many cells it has) int totElems; // holds the total number of elements in the entire table int* bucketSize; // holds the total number of elems in each specific hash table cell}; //=========================  Implementation  ================================// template<class ItemType>HashTable<ItemType>::HashTable(int hashSze){ hashSize = hashSze; head = new node*[hashSize]; bucketSize = new int[hashSize]; for(int x=0; x < hashSize; ++x) { head[x] = NULL; bucketSize[x] = 0; } totElems = 0;}/* End of HashTable */ template<class ItemType>bool HashTable<ItemType>::IsEmpty(int key){ if(key >=0 && key < hashSize) { return head[key] == NULL; } return true;}/* End of IsEmpty */ template<class ItemType>bool HashTable<ItemType>::IsFull(){ try { node* location = new node; delete location; return false; } catch(std::bad_alloc&) { return true; }}/* End of IsFull */ template<class ItemType>int HashTable<ItemType>::Hash(ItemType newItem){ long h = 19937; std::stringstream convert;  // convert the parameter to a string using "stringstream" which is done // so we can hash multiple datatypes using only one function convert << newItem; std::string temp = convert.str();  for(unsigned x=0; x < temp.length(); ++x) { h = (h << 6) ^ (h >> 26) ^ temp[x]; } return abs(h % hashSize);} /* End of Hash */ template<class ItemType>void HashTable<ItemType>::Insert(ItemType newItem){ if(IsFull()) {        //std::cout<<"nINSERT ERROR - HASH TABLE FULLn"; } else { int key = Hash(newItem); Append(key,newItem); }}/* End of Insert */ template<class ItemType>void HashTable<ItemType>::Append(int key, ItemType newItem){ if(IsFull()) {        //std::cout<<"nAPPEND ERROR - HASH TABLE FULLn"; } else { node* newNode = new node;  // adds new node newNode-> currentItem = newItem; newNode-> next = NULL; if(IsEmpty(key)) { head[key] = newNode; } else { node* tempPtr = head[key]; while(tempPtr-> next != NULL) { tempPtr = tempPtr-> next; } tempPtr-> next = newNode; } ++bucketSize[key]; ++totElems; }}/* End of Append */ template<class ItemType>bool HashTable<ItemType>::Remove(ItemType deleteItem, int key) { bool isFound = false; node* tempPtr; if(key == -1) { key = Hash(deleteItem); }      if(IsEmpty(key))    {        //std::cout<<"nREMOVE ERROR - HASH TABLE EMPTYn";    }    else if(head[key]->currentItem == deleteItem)    {        tempPtr = head[key];        head[key] = head[key]-> next;        delete tempPtr;        --totElems;        --bucketSize[key];        isFound = true;    }    else    {                 for(tempPtr = head[key];tempPtr->next!=NULL;tempPtr=tempPtr->next)        {            if(tempPtr->next->currentItem == deleteItem)            {                node* deleteNode = tempPtr->next;                tempPtr-> next = tempPtr-> next-> next;                delete deleteNode;                isFound = true;                --totElems;                --bucketSize[key];                break;            }        }            } return isFound;}/* End of Remove */ template<class ItemType>void HashTable<ItemType>::Sort(int key){     if(IsEmpty(key))    {        //std::cout<<"nSORT ERROR - HASH TABLE EMPTYn";    }    else    {         int listSize = BucketSize(key);        bool sorted = false;         do{            sorted = true;            int x = 0;            for(node* tempPtr = head[key];                tempPtr->next!=NULL && x < listSize-1;                tempPtr=tempPtr->next,++x)            {                if(tempPtr-> currentItem > tempPtr->next->currentItem)                {                    ItemType temp = tempPtr-> currentItem;                    tempPtr-> currentItem = tempPtr->next->currentItem;                    tempPtr->next->currentItem = temp;                    sorted = false;                }            }            --listSize;        }while(!sorted);    }}/* End of Sort */ template<class ItemType>int HashTable<ItemType>::TableSize(){    return hashSize;}/* End of TableSize */ template<class ItemType>int HashTable<ItemType>::TotalElems(){    return totElems;}/* End of TotalElems */ template<class ItemType>int HashTable<ItemType>::BucketSize(int key){ return(!IsEmpty(key)) ? bucketSize[key]:0;}/* End of BucketSize */ template<class ItemType>int HashTable<ItemType>::Count(ItemType searchItem) { int key = Hash(searchItem); int search = 0;      if(IsEmpty(key))    {        //std::cout<<"nCOUNT ERROR - HASH TABLE EMPTYn";    }    else    {                 for(node* tempPtr = head[key];tempPtr!=NULL;tempPtr=tempPtr->next)        {            if(tempPtr->currentItem == searchItem)            {                ++search;            }        }            } return search;}/* End of Count */ template<class ItemType>void HashTable<ItemType>::MakeEmpty(){    totElems = 0;    for(int x=0; x < hashSize; ++x)    {         if(!IsEmpty(x))        {            //std::cout << "Destroying nodes ...n";            while(!IsEmpty(x))            {                node* temp = head[x];                //std::cout << temp-> currentItem <<std::endl;                head[x] = head[x]-> next;                delete temp;            }         }        bucketSize[x] = 0;    }}/* End of MakeEmpty */ template<class ItemType>HashTable<ItemType>::~HashTable() { MakeEmpty(); delete[] head; delete[] bucketSize;}/* End of ~HashTable */ //   END OF THE HASH TABLE CLASS// -----------------------------------------------------------//   START OF THE HASH TABLE ITERATOR CLASS template <class ItemType>class HashTable<ItemType>::Iterator : public std::iterator<std::forward_iterator_tag,ItemType>, public HashTable<ItemType> {public: // Iterator constructor Iterator(node* otherIter = NULL) { itHead = otherIter; } ~Iterator() {} // The assignment and relational operators are straightforward Iterator& operator=(const Iterator& other) { itHead = other.itHead; return(*this); } bool operator==(const Iterator& other)const { return itHead == other.itHead; } bool operator!=(const Iterator& other)const { return itHead != other.itHead; } bool operator<(const Iterator& other)const { return itHead < other.itHead; } bool operator>(const Iterator& other)const { return other.itHead < itHead; } bool operator<=(const Iterator& other)const { return (!(other.itHead < itHead)); } bool operator>=(const Iterator& other)const { return (!(itHead < other.itHead)); } // Update my state such that I refer to the next element in the // HashTable. Iterator operator+(int incr) { node* temp = itHead; for(int x=0; x < incr && temp!= NULL; ++x) { temp = temp->next; } return temp; } Iterator operator+=(int incr) { for(int x=0; x < incr && itHead!= NULL; ++x) { itHead = itHead->next; } return itHead; } Iterator& operator++() // pre increment { if(itHead != NULL) { itHead = itHead->next; } return(*this); } Iterator operator++(int) // post increment { node* temp = itHead; this->operator++(); return temp; } ItemType& operator[](int incr) { // Return "junk" data // to prevent the program from crashing if(itHead == NULL || (*this + incr) == NULL) { return junk; } return(*(*this + incr)); } // Return a reference to the value in the node.  I do this instead // of returning by value so a caller can update the value in the // node directly. ItemType& operator*() { // Return "junk" data // to prevent the program from crashing if(itHead == NULL) { return junk; } return itHead->currentItem; } ItemType* operator->() { return(&**this); }private: node* itHead; ItemType junk;}; #endif // http://programmingnotes.org/ ```

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The iterator class starts on line #368, and is built to support most of the standard relational operators, as well as arithmetic operators such as ‘+,+=,++’ (pre/post increment). The * (star), bracket [] and -> arrow operators are also supported. Click here for an overview demonstrating how custom iterators can be built.

The rest of the code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Looking for sample code for a Hash Map? Click here!

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as many of its STL template class counterparts. Here are sample programs demonstrating its use.

``` #1 - Demonstrate Basic Use C++ // DEMONSTRATE USE OF THE REMOVE AND SORT FUNCTIONS #include <iostream> #include <ctime> #include <string> #include <cstdlib> #include <iomanip> #include "HashTable.h" using namespace std; // iterator declarations typedef HashTable<string>::Iterator strIterDec; // hash table size const int TABLE_SIZE = 5; int main() { // delcare variables srand(time(NULL)); const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang", "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary", "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi", "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza", "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella", "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna", "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel", "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie", "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria", "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch", "Kenneth","Perkins","Kaleena"}; int nameLen = sizeof(names)/sizeof(names[0]); // Hash table class declarations HashTable<string> strHash(TABLE_SIZE); // insert 10 items into each hash table for(int x=0; x < (TABLE_SIZE*2); ++x) { // place all data in bucket 0 // NOTE: you dont want to place all data into one // bucket, this is done for demo purposes only // Normally use the "Insert" function instead strHash.Append(0,names[rand()%(nameLen-1)]); } // assign the iterator to bucket 0 strIterDec it = strHash.begin(0); // display bucket size cout<<"Bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl; // display the first item cout<<"The first element in bucket #0 is "<< it[0] <<endl; // remove the first item in bucket 0 // NOTE: the second parameter is optional // but since we know we want bucket 0, we use it here strHash.Remove(it[0],0); // update the iterator to the new table state it = strHash.begin(0); // display the new first item cout<<"nNow bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl; cout<<"The first element in bucket #0 is "<< it[0] <<endl; // display all the items within the "strHash" table cout<<"nThe unsorted items in strHash bucket #0:n"; for(int x=0; x < strHash.BucketSize(0); ++x) { cout << "it[] = " << it[x] << endl; } // sort the items in bucket 0 strHash.Sort(0); // display all the items within the "strHash" table cout<<"nThe sorted items in strHash bucket #0:n"; for(int x=0; x < strHash.BucketSize(0); ++x) { cout << "it[] = " << it[x] << endl; } return 0; }// http://programmingnotes.org/ 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586 // DEMONSTRATE USE OF THE REMOVE AND SORT FUNCTIONS#include <iostream>#include <ctime>#include <string>#include <cstdlib>#include <iomanip>#include "HashTable.h"using namespace std; // iterator declarationstypedef HashTable<string>::Iterator strIterDec; // hash table sizeconst int TABLE_SIZE = 5; int main(){ // delcare variables srand(time(NULL)); const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",        "Kenneth","Perkins","Kaleena"};  int nameLen = sizeof(names)/sizeof(names[0]);   // Hash table class declarations HashTable<string> strHash(TABLE_SIZE);  // insert 10 items into each hash table for(int x=0; x < (TABLE_SIZE*2); ++x) { // place all data in bucket 0 // NOTE: you dont want to place all data into one // bucket, this is done for demo purposes only // Normally use the "Insert" function instead strHash.Append(0,names[rand()%(nameLen-1)]); }  // assign the iterator to bucket 0 strIterDec it = strHash.begin(0);  // display bucket size cout<<"Bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl;  // display the first item cout<<"The first element in bucket #0 is "<< it[0] <<endl;   // remove the first item in bucket 0 // NOTE: the second parameter is optional // but since we know we want bucket 0, we use it here strHash.Remove(it[0],0);  // update the iterator to the new table state it = strHash.begin(0);  // display the new first item cout<<"nNow bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl; cout<<"The first element in bucket #0 is "<< it[0] <<endl;  // display all the items within the "strHash" table cout<<"nThe unsorted items in strHash bucket #0:n"; for(int x=0; x < strHash.BucketSize(0); ++x) { cout << "it[] = " << it[x] << endl; }  // sort the items in bucket 0 strHash.Sort(0);  // display all the items within the "strHash" table cout<<"nThe sorted items in strHash bucket #0:n"; for(int x=0; x < strHash.BucketSize(0); ++x) { cout << "it[] = " << it[x] << endl; }  return 0;}// http://programmingnotes.org/ ```

SAMPLE OUTPUT:

```Bucket #0 has 10 items The first element in bucket #0 is Homer```

``` Now bucket #0 has 9 items The first element in bucket #0 is Tamra The unsorted items in strHash bucket #0: it[] = Tamra it[] = Lyndon it[] = Johanna it[] = Perkins it[] = Alva it[] = Jordon it[] = Neville it[] = Lawrence it[] = Jetta ```

```The sorted items in strHash bucket #0: it[] = Alva it[] = Jetta it[] = Johanna it[] = Jordon it[] = Lawrence it[] = Lyndon it[] = Neville it[] = Perkins it[] = Tamra ```

``` #2 - Display Items C++ // DISPLAY ALL DATA INSIDE TABLE USING STD::STRING / INT / STRUCT #include <iostream> #include <ctime> #include <string> #include <cstdlib> #include <iomanip> #include "HashTable.h" using namespace std; // sample struct demo struct MyStruct { string name; }; // iterator declarations typedef HashTable<string>::Iterator strIterDec; typedef HashTable<int>::Iterator intIterDec; typedef HashTable<MyStruct>::Iterator strctIterDec; // hash table size const int TABLE_SIZE = 10; int main() { // delcare variables srand(time(NULL)); const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang", "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary", "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi", "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza", "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella", "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna", "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel", "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie", "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria", "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch", "Kenneth","Perkins","Kaleena"}; int nameLen = sizeof(names)/sizeof(names[0]); // Hash table class declarations HashTable<string> strHash(TABLE_SIZE); HashTable<int> intHash = TABLE_SIZE; HashTable<MyStruct> strctHash = TABLE_SIZE; // access struct element MyStruct strctAccess; // insert 20 items into each hash table for(int x=0; x < (TABLE_SIZE*2); ++x) { // Use the "insert" function to place data into the hash table // this function automatically hashes the basic datatypes // i.e: int, double, char, char*, string strHash.Insert(names[rand()%(nameLen-1)]); intHash.Insert(rand()%10000); // The "insert" function cant be used on a struct, so we // use the "append" function for the struct declaration. // We use the "strHash" class declaration to use its // hash function, then place the struct in an appropriate // hashed bucket strctAccess.name = names[rand()%(nameLen-1)]; int strctHashKey = strHash.Hash(strctAccess.name); strctHash.Append(strctHashKey,strctAccess); } // display all the items within the "strHash" table for(int x=0; x < strHash.TableSize(); ++x) { if(!strHash.IsEmpty(x)) { cout<<"nstrHash Bucket #"<<x<<":n"; for(strIterDec it = strHash.begin(x); it != strHash.end(x); it+=1) { // access elements using the * (star) operator cout << "*it = " << *it << endl; } } } // creates a line seperator cout<<endl; cout.fill('-'); cout<<left<<setw(80)<<""<<endl; // display all the items within the "intHash" table for(int x=0; x < intHash.TableSize(); ++x) { intIterDec it = intHash.begin(x); if(!intHash.IsEmpty(x)) { cout<<"nintHash Bucket #"<<x<<":n"; for(int y = 0; y < intHash.BucketSize(x); ++y) { // access elements using the [] operator cout << "it[] = " << it[y] << endl; } } } // creates a line seperator cout<<endl; cout.fill('-'); cout<<left<<setw(80)<<""<<endl; // display all the items within the "strctHash" table for(int x=0; x < strctHash.TableSize(); ++x) { if(!strctHash.IsEmpty(x)) { cout<<"nstrctHash Bucket #"<<x<<":n"; for(strctIterDec it = strctHash.begin(x); it!=strctHash.end(x); it=it+1) { // access struct/class elements using the -> operator cout << "it-> = " << it->name << endl; } } } return 0; }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122 // DISPLAY ALL DATA INSIDE TABLE USING STD::STRING / INT / STRUCT#include <iostream>#include <ctime>#include <string>#include <cstdlib>#include <iomanip>#include "HashTable.h"using namespace std; // sample struct demostruct MyStruct{ string name;}; // iterator declarationstypedef HashTable<string>::Iterator strIterDec;typedef HashTable<int>::Iterator intIterDec;typedef HashTable<MyStruct>::Iterator strctIterDec; // hash table sizeconst int TABLE_SIZE = 10; int main(){ // delcare variables srand(time(NULL)); const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",        "Kenneth","Perkins","Kaleena"};     int nameLen = sizeof(names)/sizeof(names[0]);   // Hash table class declarations HashTable<string> strHash(TABLE_SIZE); HashTable<int> intHash = TABLE_SIZE; HashTable<MyStruct> strctHash = TABLE_SIZE;  // access struct element MyStruct strctAccess;   // insert 20 items into each hash table for(int x=0; x < (TABLE_SIZE*2); ++x) { // Use the "insert" function to place data into the hash table // this function automatically hashes the basic datatypes // i.e: int, double, char, char*, string strHash.Insert(names[rand()%(nameLen-1)]); intHash.Insert(rand()%10000);  // The "insert" function cant be used on a struct, so we // use the "append" function for the struct declaration. // We use the "strHash" class declaration to use its // hash function, then place the struct in an appropriate // hashed bucket strctAccess.name = names[rand()%(nameLen-1)]; int strctHashKey = strHash.Hash(strctAccess.name); strctHash.Append(strctHashKey,strctAccess); }  // display all the items within the "strHash" table for(int x=0; x < strHash.TableSize(); ++x) { if(!strHash.IsEmpty(x)) { cout<<"nstrHash Bucket #"<<x<<":n"; for(strIterDec it = strHash.begin(x); it != strHash.end(x); it+=1) { // access elements using the * (star) operator cout << "*it = " << *it << endl; } } } // creates a line seperator cout<<endl; cout.fill('-'); cout<<left<<setw(80)<<""<<endl;  // display all the items within the "intHash" table for(int x=0; x < intHash.TableSize(); ++x) { intIterDec it = intHash.begin(x); if(!intHash.IsEmpty(x)) { cout<<"nintHash Bucket #"<<x<<":n"; for(int y = 0; y < intHash.BucketSize(x); ++y) { // access elements using the [] operator cout << "it[] = " << it[y] << endl; } } }  // creates a line seperator cout<<endl; cout.fill('-'); cout<<left<<setw(80)<<""<<endl;  // display all the items within the "strctHash" table for(int x=0; x < strctHash.TableSize(); ++x) { if(!strctHash.IsEmpty(x)) { cout<<"nstrctHash Bucket #"<<x<<":n"; for(strctIterDec it = strctHash.begin(x); it!=strctHash.end(x); it=it+1) { // access struct/class elements using the -> operator cout << "it-> = " << it->name << endl; } } }  return 0;}// http://programmingnotes.org/ ```

SAMPLE OUTPUT:

``` strHash Bucket #0: *it = Cinderella *it = Perkins *it = Krystal *it = Roger *it = Roger```

``` strHash Bucket #1: *it = Lilliam *it = Lilliam *it = Theda strHash Bucket #2: *it = Arie strHash Bucket #3: *it = Magda strHash Bucket #6: *it = Edda *it = Irvin *it = Kati *it = Lyndon strHash Bucket #7: *it = Deb *it = Jaime strHash Bucket #8: *it = Neville *it = Victoria strHash Bucket #9: *it = Chery *it = Evelia -------------------------------------------- intHash Bucket #0: it[] = 2449 it[] = 6135 intHash Bucket #1: it[] = 1120 it[] = 852 intHash Bucket #2: it[] = 5727 intHash Bucket #3: it[] = 1174 intHash Bucket #4: it[] = 2775 it[] = 3525 it[] = 8375 intHash Bucket #5: it[] = 4322 it[] = 8722 it[] = 5016 intHash Bucket #6: it[] = 5053 it[] = 7231 it[] = 1571 intHash Bucket #7: it[] = 1666 it[] = 4510 it[] = 1548 it[] = 3646 intHash Bucket #9: it[] = 2756 -------------------------------------------- strctHash Bucket #0: it-> = Cherilyn it-> = Roger strctHash Bucket #1: it-> = Tamra it-> = Alex it-> = Theda strctHash Bucket #2: it-> = Nigel it-> = Alva it-> = Arie strctHash Bucket #4: it-> = Basil strctHash Bucket #5: it-> = Tod strctHash Bucket #6: it-> = Irvin it-> = Lyndon strctHash Bucket #7: it-> = Amina it-> = Hillary it-> = Kenneth it-> = Amina strctHash Bucket #8: it-> = Gene it-> = Lemuel it-> = Gene ```

```strctHash Bucket #9: it-> = Albertina ```

## Java || Snippet – How To Read & Write Data From A File

This page will consist of a demonstration of a simple quadratic formula program, which highlights the use of the input/output mechanisms of manipulating a text file. This program will read in data from a file (numbers), manipulate that data, and output new data into a different text file.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

```Try/Catch - What Is It? The "Math" Class - sqrt and pow The "Scanner" Class - Used for the input file The "FileWriter" Class - Used for the output file The "File" Class - Used to locate the input/output files Working With Files ```

NOTE: The data file that is used in this example can be downloaded here.

In order to read in the data .txt file, you need to save the .txt file in the same directory (or folder) as your .java file is saved in. If you are using Eclipse, the default directory will probably be:

``` Documents > Workspace > [Your project name] ```

Alternatively, you can execute this command, which will give you the current directory in which your source file resides:

``` System.out.println(System.getProperty("user.dir")); ```

Whatever the case, in order to read in the data .txt file, your program must know where it is located on the system.

``` Input/Output Manipulation Java import java.io.File; // used to locate the input/output files import java.io.FileWriter; // used for file output import java.util.Scanner; // used for file input public class ReadWriteFile { public static void main(String[] args) { // declare & initialize variables Scanner infile; FileWriter outfile; double a=0,b=0,c=0; double root1=0, root2=0; System.out.println("Welcome to My Programming Notes' Java Program.n"); // use a try/catch to check to see if the input file exists, & if not then EXIT try { // this opens the input file // YOUR INPUT FILE NAME GOES BELOW infile = new Scanner(new File("INPUT_Quadratic_programmingnotes_freeweq_com.txt")); // this opens the output file // if the file doesnt already exist, it will be created outfile = new FileWriter(new File("OUTPUT_Quadratic_programmingnotes_freeweq_com.txt")); // if the file was found, this try/catch will execute, and the loop will // attempt to get the 3 numbers from the input file and place // them inside the variables 'a,b,c' try { while(infile.hasNext()) { // this assigns the incoming data to the // variables 'a', 'b' and 'c' // NOTE: it is just like a normal scanner statement a = infile.nextInt(); b = infile.nextInt(); c = infile.nextInt(); // NOTE: if you want to read in data into an array // your declaration would be like this // ------------------------------------ // a[counter] = infile.nextInt(); // b[counter] = infile.nextInt(); // c[counter] = infile.nextInt(); // ++counter; } } catch(Exception e) { // if there was an error on input, (i.e the input file contains letters) // this block will execite, and the program will exit System.err.println("There is a formatting error in the input file!n" + "The input file should contain only 3 numbersn"); System.exit(1); } // this does the quadratic formula calculations root1 = ((-b) + Math.sqrt(Math.pow(b,2) - (4*a*c)))/(2*a); root2 = ((-b) - Math.sqrt(Math.pow(b,2) - (4*a*c)))/(2*a); // this displays the numbers to screen via stdout System.out.println("For the numbers:na = "+a+"nb = "+b+"nc = "+c); System.out.println("nroot 1 = "+root1+"nroot 2 = "+root2); // this saves the data to the output file // NOTE: its almost exactly the same as the above print statement, except // the 'write' function is dependent on the "newline" (NL) method // to generate a line break String NL = System.getProperty("line.separator"); outfile.write("For the numbers:"+NL+"a = "+a+NL+"b = "+b+NL+"c = "+c); outfile.write(NL+NL+"root 1 = "+root1+NL+"root 2 = "+root2); // close the input/output files once you are done using them infile.close(); outfile.close(); } catch(Exception e) { // if the file cannot be found, this block will execute, and the // program will exit System.err.println("Error, the input file could not be found!n" +e.getMessage()); System.exit(1); } System.out.println("nProgram Success!!n"); }// end of main }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990 import java.io.File; // used to locate the input/output filesimport java.io.FileWriter; // used for file outputimport java.util.Scanner; // used for file input public class ReadWriteFile{ public static void main(String[] args) { // declare & initialize variables Scanner infile; FileWriter outfile; double a=0,b=0,c=0; double root1=0, root2=0; System.out.println("Welcome to My Programming Notes' Java Program.n"); // use a try/catch to check to see if the input file exists, & if not then EXIT try { // this opens the input file // YOUR INPUT FILE NAME GOES BELOW infile = new Scanner(new File("INPUT_Quadratic_programmingnotes_freeweq_com.txt")); // this opens the output file // if the file doesnt already exist, it will be created outfile = new FileWriter(new File("OUTPUT_Quadratic_programmingnotes_freeweq_com.txt")); // if the file was found, this try/catch will execute, and the loop will // attempt to get the 3 numbers from the input file and place // them inside the variables 'a,b,c' try { while(infile.hasNext()) { // this assigns the incoming data to the // variables 'a', 'b' and 'c' // NOTE: it is just like a normal scanner statement a = infile.nextInt(); b = infile.nextInt(); c = infile.nextInt(); // NOTE: if you want to read in data into an array // your declaration would be like this // ------------------------------------ // a[counter] = infile.nextInt(); // b[counter] = infile.nextInt(); // c[counter] = infile.nextInt(); // ++counter; } } catch(Exception e) { // if there was an error on input, (i.e the input file contains letters) // this block will execite, and the program will exit System.err.println("There is a formatting error in the input file!n" + "The input file should contain only 3 numbersn"); System.exit(1); } // this does the quadratic formula calculations root1 = ((-b) + Math.sqrt(Math.pow(b,2) - (4*a*c)))/(2*a); root2 = ((-b) - Math.sqrt(Math.pow(b,2) - (4*a*c)))/(2*a); // this displays the numbers to screen via stdout System.out.println("For the numbers:na = "+a+"nb = "+b+"nc = "+c); System.out.println("nroot 1 = "+root1+"nroot 2 = "+root2); // this saves the data to the output file // NOTE: its almost exactly the same as the above print statement, except // the 'write' function is dependent on the "newline" (NL) method // to generate a line break String NL = System.getProperty("line.separator"); outfile.write("For the numbers:"+NL+"a = "+a+NL+"b = "+b+NL+"c = "+c); outfile.write(NL+NL+"root 1 = "+root1+NL+"root 2 = "+root2); // close the input/output files once you are done using them infile.close(); outfile.close(); } catch(Exception e) { // if the file cannot be found, this block will execute, and the // program will exit System.err.println("Error, the input file could not be found!n" +e.getMessage()); System.exit(1); } System.out.println("nProgram Success!!n"); }// end of main }// http://programmingnotes.org/ ```

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output
(Remember to include the example input file)

`Welcome to My Programming Notes' Java Program.`

``` For the numbers: a = 2.0 b = 4.0 c = -16.0 root 1 = 2.0 root 2 = -4.0 ```

```Program Success!! ```

## C++ || Snippet – Simple Linked List Using Delete, Insert, & Display Functions

The following is sample code for a simple linked list, which implements the following functions: “Delete, Insert, and Display.”

The sample code provided on this page is a stripped down version of a more robust linked list class which was previously discussed on this site. Sample code for that can be found here.

It is recommended you check that out as the functions implemented within that class are very useful.

``` Simple Linked List C++ // ============================================================================ // Author: K Perkins // Date: Aug 18, 2012 // Taken From: http://programmingnotes.org/ // File: SimpleList.cpp // Description: Demonstrates the use of a simple linked list. // ============================================================================ #include <iostream> #include <string> using namespace std; struct node { /* -- you can use different data types here -- instead of just a string char letter; int number; double fNumber; */ string name; node* next; }; // global variables // this is the front of the list node* head = NULL; // function prototype void Insert(string info); void Delete(string info); void Display(); void DestroyList(); int main() { // if you want to insert data into the list // this is one way you can do it, using a 'temp' pointer node* temp = new node; temp-> name = "My Programming Notes"; temp-> next = NULL; // set the head node to the data thats in the 'temp' pointer head = temp; // display data to the screen cout << head->name <<endl<<endl; // use the insert function to add new data to the list // NOTE: you could have also used the 'insert' function ^ above // to place data into the list Insert("Is An Awesome Site!"); // insert more data into the list Insert("August"); Display(); // delete the selected text from the list Delete("August"); Display(); // destroy the current pointers in the list // after you are finished using them DestroyList(); return 0; }// end of main void Insert(string info) { node* newItem = new node; newItem-> name = info; newItem-> next = NULL; // if the list is empty, add new item to the front if(head == NULL) { head = newItem; } else // if the list isnt empty, add new item to the end { node* iter = head; while(iter->next != NULL) { iter = iter-> next; } iter-> next = newItem; } }// end of Insert void Delete(string info) { node* iter = head; // if the list is empty, do nothing if(head == NULL) { return; } // delete the first item in the list else if(head->name == info) { head = head-> next; delete iter; } // search the list until we find the desired item else { while(iter->next != NULL) { if(iter->next->name == info) { node* deleteNode = iter->next; iter-> next = iter-> next-> next; delete deleteNode; break; } iter = iter->next; } } }// end of Delete void Display() { node* iter = head; // traverse thru the list, displaying the // text at each node location while(iter != NULL) { cout<<iter->name<<endl; iter = iter-> next; } cout<<endl; }// end of Display void DestroyList() { if(head != NULL) { cout << "nnDestroying nodes...n"; while(head != NULL) { node* temp = head; cout << temp-> name << 'n'; head = head-> next; delete temp; } } }// http://programmingnotes.org/ 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147```