Tag Archives: if/else
C++ || Simple 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 C++.
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.
REQUIRED KNOWLEDGE FOR THIS PROGRAM
How To Convert Infix To Postfix
How To Evaluate A Postfix Expression
1. Overview
The program demonstrated on this page is different from a previous implementation of the same type in that this version does not use a Finite State Machine during the conversion process, which simplifies the implemetation!
This program has the following flow of control:
• Get an infix expression from the user
• Convert the infix expression to postfix & 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 by breaking the infix string into tokens found from the above step
• Display the evaluated answer to the screen
The above steps are implemented below.
2. Infix To Posfix Conversion & Evaluation
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// ============================================================================ // Author: Kenneth Perkins // Date: Jan 31, 2014 // Updated: Feb 5, 2021 // Taken From: http://programmingnotes.org/ // File: InToPostEval.cpp // Description: The following demonstrates the implementation of an infix to // postfix converter and evaluator. 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> #include <algorithm> #include <exception> #include <stdexcept> // function prototypes void displayDirections(); std::string convertInfixToPostfix(std::string infix); bool isMathOperator(char token); int orderOfOperations(char token); double evaluatePostfix(const std::string& postfix); double calculate(char mathOperator, double value1, double value2); bool isNumeric(char value); bool isNumeric(std::string value); std::vector<std::string> split(const std::string& source, const std::string& delimiters = " "); std::string replaceAll(const std::string& source , const std::string& oldValue, const std::string& newValue); int main() { // declare variables std::string infix = ""; // display directions to user displayDirections(); try { // get data from user std::cout << "\nPlease enter an Infix expression: "; std::getline(std::cin, infix); // convert infix to postfix std::string postfix = convertInfixToPostfix(infix); std::cout << "\nThe Infix expression = " << infix; std::cout << "\nThe Postfix expression = " << postfix << std::endl; // evaluate the postfix string double answer = evaluatePostfix(postfix); std::cout << "\nFinal answer = " << answer << std::endl; } catch (std::exception& e) { std::cout << "\nAn error occurred: " + std::string(e.what()) << std::endl; } std::cin.get(); return 0; }// end of main void displayDirections() { // this function displays instructions to the screen std::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 std::string convertInfixToPostfix(std::string infix) { // this function converts an infix expression to postfix // declare function variables std::string postfix; std::stack<char> charStack; // remove all whitespace from the string infix.erase(std::remove_if(infix.begin(), infix.end(), [](char c) { return std::isspace(static_cast<unsigned char>(c)); }), infix.end()); // negate equations marked with '--' infix = replaceAll(infix, "(--", "("); // automatically convert negative numbers to have the ~ symbol. // this is done so we can distinguish negative numbers and the subtraction symbol for (unsigned x = 0; x < infix.length(); ++x) { if (infix[x] != '-') { continue; } if (x == 0 || infix[x - 1] == '(' || isMathOperator(infix[x - 1])) { infix[x] = '~'; } } // 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 (isNumeric(infix[x])) { if (postfix.length() > 0 && !isNumeric(postfix.back())) { if (!std::isspace(postfix.back())) { postfix += " "; } } postfix += infix[x]; } else if (std::isspace(infix[x])) { continue; } else if (isMathOperator(infix[x])) { if (postfix.length() > 0 && !std::isspace(postfix.back())) { 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 if (postfix.length() > 0 && !std::isspace(postfix.back())) { postfix += " "; } 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() != '(')) { if (postfix.length() > 0 && !std::isspace(postfix.back())) { postfix += " "; } // 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(); } // pop '(' symbol off the stack if (!charStack.empty()) { charStack.pop(); } else { // no matching '(' throw std::invalid_argument{ "PARENTHESES MISMATCH" }; } } else { throw std::invalid_argument{ "INVALID INPUT" }; } } // place any remaining math operators from the stack onto // the postfix array while (!charStack.empty()) { if (charStack.top() == '(' || charStack.top() == ')') { throw std::invalid_argument{ "PARENTHESES MISMATCH" }; } if (postfix.length() > 0 && !std::isspace(postfix.back())) { postfix += " "; } postfix += charStack.top(); charStack.pop(); } // replace all '~' symbols with a minus sign postfix = replaceAll(postfix, "~", "-"); return postfix; }// end of convertInfixToPostfix bool isMathOperator(char token) { // this function checks if operand is a math operator switch (std::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 (std::tolower(token)) { case 'c': case 's': case 't': priority = 5; break; case '^': case '$': priority = 4; break; case '*': case '/': case '%': priority = 3; break; case '-': priority = 2; break; case '+': priority = 1; break; } return priority; }// end of orderOfOperations double evaluatePostfix(const std::string& postfix) { // this function evaluates a postfix expression // declare function variables double answer = 0; std::stack<double> doubleStack; // split string into tokens to isolate multi digit, negative and decimal // numbers, aswell as single digit numbers and math operators auto tokens = split(postfix); // display the found tokens to the screen //for (unsigned x = 0; x < tokens.size(); ++x) { // std::cout<< tokens.at(x) << std::endl; //} std::cout << "\nCalculations:\n"; // loop thru array until there is no more data for (unsigned x = 0; x < tokens.size(); ++x) { auto token = tokens[x]; // push numbers & negative numbers onto the stack if (isNumeric(token)) { doubleStack.push(std::atof(token.c_str())); } // if expression is a math operator, pop numbers from stack // & send the popped numbers to the 'calculate' function else if (isMathOperator(token[0]) && (!doubleStack.empty())) { double value1 = 0; double value2 = 0; char mathOperator = static_cast<unsigned char>(std::tolower(token[0])); // if expression is square root, sin, cos, // or tan operation only pop stack once if (mathOperator == '$' || mathOperator == 's' || mathOperator == 'c' || mathOperator == 't') { value2 = 0; value1 = doubleStack.top(); doubleStack.pop(); answer = calculate(mathOperator, value1, value2); doubleStack.push(answer); } else if (doubleStack.size() > 1) { value2 = doubleStack.top(); doubleStack.pop(); value1 = doubleStack.top(); doubleStack.pop(); answer = calculate(mathOperator, value1, value2); doubleStack.push(answer); } } else { // this should never execute, & if it does, something went really wrong throw std::invalid_argument{ "INVALID POSTFIX STRING" }; } } // 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 mathOperator, double value1, double value2) { // this function carries out the actual math process double ans = 0; switch (std::tolower(mathOperator)) { case '+': std::cout << value1 << mathOperator << value2; ans = value1 + value2; break; case '-': std::cout << value1 << mathOperator << value2; ans = value1 - value2; break; case '*': std::cout << value1 << mathOperator << value2; ans = value1 * value2; break; case '/': std::cout << value1 << mathOperator << value2; ans = value1 / value2; break; case '%': std::cout << value1 << mathOperator << value2; ans = ((int)value1 % (int)value2) + std::modf(value1, &value2); break; case '^': std::cout << value1 << mathOperator << value2; ans = std::pow(value1, value2); break; case '$': std::cout << char(251) << value1; ans = std::sqrt(value1); break; case 'c': std::cout << "cos(" << value1 << ")"; ans = std::cos(value1); break; case 's': std::cout << "sin(" << value1 << ")"; ans = std::sin(value1); break; case 't': std::cout << "tan(" << value1 << ")"; ans = std::tan(value1); break; default: ans = 0; break; } std::cout << " = " << ans << std::endl; return ans; }// end of calculate std::vector<std::string> split(const std::string& source, const std::string& delimiters) { std::size_t prev = 0; std::size_t currentPos = 0; std::vector<std::string> results; while ((currentPos = source.find_first_of(delimiters, prev)) != std::string::npos) { if (currentPos > prev) { results.push_back(source.substr(prev, currentPos - prev)); } prev = currentPos + 1; } if (prev < source.length()) { results.push_back(source.substr(prev, std::string::npos)); } return results; }// end of split std::string replaceAll(const std::string& source , const std::string& oldValue, const std::string& newValue) { if (oldValue.empty()) { return source; } std::string newString; newString.reserve(source.length()); std::size_t lastPos = 0; std::size_t findPos; while (std::string::npos != (findPos = source.find(oldValue, lastPos))) { newString.append(source, lastPos, findPos - lastPos); newString += newValue; lastPos = findPos + oldValue.length(); } newString += source.substr(lastPos); return newString; }// end of replaceAll bool isNumeric(char value) { return std::isdigit(value) || value == '.' || value == '~'; }// end of isNumeric bool isNumeric(std::string value) { for (unsigned index = 0; index < value.length(); ++index) { if (index == 0 && value[index] == '-' && value.length() > 1) { continue; } if (!isNumeric(value[index])) { return false; } } return true; }// 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 = 36Final 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 = -238.466Final 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 ^ s 1.4 * 23 2 + $ -2.8 - / 1 2 % c 7.28 .1987 * 23 t ^ / *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 = 0.00855389Final answer = 0.00855389
====== RUN 4 ======
==== 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: (1987 + 1991) * -1
The Infix expression = (1987 + 1991) * -1
The Postfix expression = 1987 1991 + -1 *Calculations:
1987+1991 = 3978
3978*-1 = -3978Final answer = -3978
====== RUN 5 ======
==== 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: (1+(2*((3+(4*5))*6)))
The Infix expression = (1+(2*((3+(4*5))*6)))
The Postfix expression = 1 2 3 4 5 * + 6 * * +Calculations:
4*5 = 20
3+20 = 23
23*6 = 138
2*138 = 276
1+276 = 277Final answer = 277
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 on the postfix string. This is used to differentiate between a negative number and a subtraction 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.
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// ============================================================================ // Author: Kenneth 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> #include <algorithm> 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; cin.get(); 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; // remove all whitespace from the string infix.erase(std::remove_if(infix.begin(), infix.end(), [](char c) { return std::isspace(static_cast<unsigned char>(c)); }), infix.end()); // automatically convert negative numbers to have the ~ symbol for (unsigned x = 0; x < infix.length(); ++x) { if (infix[x] != '-') { continue; } else if (x + 1 < infix.length() && IsMathOperator(infix[x + 1])) { continue; } if (x == 0 || infix[x - 1] == '(' || IsMathOperator(infix[x - 1])) { infix[x] = '~'; } } // 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 SUCCESSFUL PARSE - If the current state in our machine == REJECT (the starting state), then we have successfully parsed a token, which is returned to its caller - ELSE we continue trying to find a successful 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 NumberSample 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 = 36Final 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 NumberSample 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 = -238.466Final 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 NumberSample 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 = 0.00855389Final answer = 0.00855389
====== RUN 4 ======
==== 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: (1987 + 1991) * -1
The Infix expression = (1987 + 1991) * -1
The Postfix expression = 1987 1991+ ~1*Calculations:
1987+1991 = 3978
3978*-1 = -3978Final answer = -3978
Python || Find The Average Using A List – Omit Highest And Lowest Scores
This page will consist of a program which calculates the average of a specific amount of numbers using a list.
REQUIRED KNOWLEDGE FOR THIS PROGRAM
Lists
For Loops
Arithmetic Operators
Basic Math - How To Find The Average
The following program is fairly simple, and was used to introduce the list concept. This program prompts the user to enter the total amount of numbers they wish to find the average for, then displays the answer to the screen. Using a sort, this program also has the ability to find the average of a list of numbers, omitting the highest and lowest valued items.
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# ============================================================================= # Author: K Perkins # Taken From: http://programmingnotes.org/ # Date: Jan 29, 2014 # File: Average.py # Description: The following demonstrates finding the average of numbers # contained in a list. # ============================================================================= # calculate the average of numbers in a list def Average(arry, size): total = 0 # traverse the list adding all the items together for x in range(size): total += arry[x] # return the average return total / size ## end of Average def main(): # declare variables arry = [] # initialize the list numElems = 0 # ask user how many items they want to place in list numElems = int(input("How many items do you want to place into the list?: ")) # print a newline print("") # user enters data into list using a for loop for x in range(0, numElems): arry.append(int(input("Enter item #%d: " % (x+1)))) # display data print("nThe current items inside the list are: ") for x in range(0, numElems): print("Item #%d: %d" % ((x+1), arry[x])) # display the average using a function print("nThe average of the %d numbers is %.2f" % (numElems, Average(arry, len(arry)))) # sort the numbers in the list from lowest to highest arry.sort() # erase the highest/lowest numbers arry.pop(len(arry)-1) arry.pop(0) # display the average using a function print("nThe average adjusted score omitting the highest and " "lowest result is %.2f" % (Average(arry, len(arry)))) ## end of main 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.
The following is sample output.
How many items do you want to place into the list?: 5Enter item #1: 7
Enter item #2: 7
Enter item #3: 4
Enter item #4: 8
Enter item #5: 7The current items inside the list are:
Item #1: 7
Item #2: 7
Item #3: 4
Item #4: 8
Item #5: 7The average of the 5 numbers is 6.60
The average adjusted score omitting the highest and lowest result is 7.00
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 ===
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// ============================================================================ // Author: Kenneth 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 FULL\n"; } 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 EMPTY\n"; } 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 EMPTY\n"; } 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 EMPTY\n"; } 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 EMPTY\n"; } 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.
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// 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/ |
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-> 462These are all of the items in the entire hash map:
Key-> CIS Value-> 465Key-> DANCE Value-> 134
Key-> PE Value-> 145
Key-> PE Value-> 125Key-> MATH Value-> 270
Key-> MATH Value-> 150Key-> GEOL Value-> 201
Key-> GEOL Value-> 101Key-> CPSC Value-> 120
Key-> CPSC Value-> 131
Key-> CPSC Value-> 240
Key-> CPSC Value-> 301
Key-> CPSC Value-> 462Key-> BIOL Value-> 585
Key-> BIOL Value-> 134Key-> ART Value-> 101
Key-> ART Value-> 345Key-> CHEM Value-> 185
Key-> HIST Value-> 251
The total number of items in the hash map is: 19
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// 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 <<"\n\tYear: "<<iter->value.year <<"\n\tMPG: "<<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 <<"\n\tYear: "<<(*iter).value.year <<"\n\tMPG: "<<(*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 <<"\n\tYear: "<<iter->value.year <<"\n\tMPG: "<<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 carsThese are all of the cars in the hash map:
Jessica's car(s)
Car: Nissan Altima
Year: 2011
MPG: 30.7Kenneth's car(s)
Car: Ford Fusion
Year: 2006
MPG: 28.5Car: BMW 535i
Year: 2014
MPG: 25.4Car: 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: 30.7Kenneth's car(s)
Car: Acura Integra
Year: 2001
MPG: 20.2Car: BMW 535i
Year: 2014
MPG: 25.4Car: 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: 30.7Kenneth's car(s)
Car: BMW 535i
Year: 2014
MPG: 25.4Car: Ford Fusion
Year: 2006
MPG: 28.5
-----------------------------------------------------The total number of cars in the hash map is: 3
Python || Using If Statements & String Variables
As previously mentioned, you can use “int” and “float” to represent numbers, but what if you want to store letters? Strings help you do that.
==== SINGLE CHAR ====
This example will demonstrate a simple program using strings, which checks to see if the user entered the correctly predefined letter.
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# ============================================================================= # Author: Kenneth Perkins # Date: May 29, 2013 # Updated: Feb 16, 2021 # Taken From: http://programmingnotes.org/ # File: char.py # Description: Demonstrates using char variables # ============================================================================= def main(): # declare variables userInput = "" # this variable is a string letter = '' # this holds the individual character # get data from user userInput = input("Please try to guess the letter I am thinking of: ") # we only want to check the first character in the string, # so we get the letter at index zero and save it into its # own variable letter = userInput[0] # use an if statement to check equality. if ((letter == 'a') or (letter == 'A')): print("\nYou have guessed correctly!") else: print("\nSorry, that was not the correct letter I was thinking of..") if __name__ == "__main__": main() # http://programmingnotes.org/ |
Notice in line 11 I declare the string data type, naming it “userInput.” I also initialized it as an empty variable. In line 23 I used an “If/Else Statement” to determine if the user entered value matches the predefined letter within the program. I also used the “OR” operator in line 23 to determine if the letter the user entered into the program was lower or uppercase. Try compiling the program simply using this
if (letter == 'a') as your if statement, and notice the difference.
The resulting code should give this as output
Please try to guess the letter I am thinking of: A
You have guessed correctly!
==== CHECK IF LETTER IS UPPER CASE ====
This example is similar to the previous one, and will check if a user entered letter is uppercase.
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# ============================================================================= # Author: Kenneth Perkins # Date: May 29, 2013 # Updated: Feb 16, 2021 # Taken From: http://programmingnotes.org/ # File: uppercase.py # Description: Demonstrates checking if a char variable is uppercase # ============================================================================= def main(): # declare variables userInput = "" # this variable is a string letter = '' # this holds the individual character # get data from user userInput = input("Please enter an UPPERCASE letter: ") # get the 1st character in the string letter = userInput[0] # check to see if entered data falls between uppercase values if ((letter >= 'A') and (letter <= 'Z')): print("\n'%c' is an is an uppercase letter!" % (letter)) else: print("\nSorry, '%c' is not an uppercase letter.." % (letter)) if __name__ == "__main__": main() # http://programmingnotes.org/ |
Notice in line 21, an If statement was used, which checks to see if the user entered data falls between letter A and letter Z. We did that by using the “AND” operator. So that IF statement is basically saying (in plain english)
IF ('letter' is equal to or greater than 'A') AND ('letter' is equal to or less than 'Z')THEN it is an uppercase letter
The resulting code should give this as output
Please enter an UPPERCASE letter: g
Sorry, 'g' is not an uppercase letter..
==== CHECK IF LETTER IS A VOWEL ====
This example will utilize more if statements, checking to see if the user entered letter is a vowel or not. This will be very similar to the previous example, utilizing the OR operator once again.
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# ============================================================================= # Author: Kenneth Perkins # Date: May 29, 2013 # Updated: Feb 16, 2021 # Taken From: http://programmingnotes.org/ # File: vowel.py # Description: Demonstrates checking if a char variable is a vowel # ============================================================================= def main(): # declare variables userInput = "" # this variable is a string letter = '' # this holds the individual character # get data from user userInput = input("Please enter a vowel: ") # get the 1st character in the string letter = userInput[0] # check to see if entered data is A,E,I,O,U,Y if ((letter == 'a')or(letter == 'A')or(letter == 'e')or (letter == 'E')or(letter == 'i')or(letter == 'I')or (letter == 'o')or(letter == 'O')or(letter == 'u')or (letter == 'U')or(letter == 'y')or(letter == 'Y')): print("\nCorrect, '%c' is a vowel!" % (letter)) else: print("\nSorry, '%c' is not a vowel.." % (letter)) if __name__ == "__main__": main() # http://programmingnotes.org/ |
This program should be very straight forward, and its basically checking to see if the user entered data is the letter A, E, I, O, U or Y.
The resulting code should give the following output
Please enter a vowel: K
Sorry, 'K' is not a vowel..
==== HELLO WORLD v2 ====
This last example will demonstrate using the string data type to print the line “Hello World!” to the screen.
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# ============================================================================= # Author: Kenneth Perkins # Date: May 29, 2013 # Updated: Feb 16, 2021 # Taken From: http://programmingnotes.org/ # File: string.py # Description: Demonstrates using string variables # ============================================================================= def main(): # declare variables userInput = "" # this variable is a string # get data from user userInput = input("Please enter a sentence: ") # display string print("\nYou Entered: '%s'" % (userInput)) if __name__ == "__main__": main() # http://programmingnotes.org/ |
The following is similar to the other examples listed on this page, except we display the entire string instead of just simply the first character.
The resulting code should give following output
Please enter a sentence: Hello World!
You Entered: 'Hello World!'
C++ || Simple Spell Checker Using A Hash Table
The following is another programming assignment which was presented in a C++ Data Structures course. This assignment was used to gain more experience using hash tables.
REQUIRED KNOWLEDGE FOR THIS PROGRAM
Hash Table - What Is It?
How To Create A Spell Checker
How To Read Data From A File
Strtok - Split Strings Into Tokens
#include 'HashTable.h'
The Dictionary File - Download Here
== OVERVIEW ==
This program first reads words from a dictionary file, and inserts them into a hash table.
The dictionary file consists of a list of 62,454 correctly spelled lowercase words, separated by whitespace. The words are inserted into the hash table, with each bucket growing dynamically as necessary to hold all of the incoming data.
After the reading of the dictionary file is complete, the program prompts the user for input. After input is obtained, each word that the user enteres into the program is looked up within the hash table to see if it exists. If the user entered word exists within the hash table, then that word is spelled correctly. If not, a list of possible suggested spelling corrections is displayed to the screen.
== HASH TABLE STATISTICS ==
To better understand how hash tables work, this program reports the following statistics to the screen:
• The total size of the hash table.
• The size of the largest hash table bucket.
• The size of the smallest hash table bucket.
• The total number of buckets used.
• The average hash table bucket size.
A timer is used in this program to time (in seconds) how long it takes to read in the dictionary file. The program also saves each hash table bucket into a separate output .txt file. This is used to further visualize how the hash table data is internally being stored within memory.
== SPELL CHECKING ==
The easiest way to generate corrections for a spell checker is via a trial and error method. If we assume that the misspelled word contains only a single error, we can try all possible corrections and look each up in the dictionary.
Example:
wird: bird gird ward word wild wind wire wiry
Traditionally, spell checkers look for four possible errors: a wrong letter (“wird”), also knows as alteration. An inserted letter (“woprd”), a deleted letter (“wrd”), or a pair of adjacent transposed letters (“wrod”).
The easiest of which is checking for a wrong letter. For example, if a word isnt found in the dictionary, all variants of that word can be looked up by changing one letter. Given the user input “wird,” a one letter variant can be “aird”, “bird”, “cird”, etc. through “zird.” Then “ward”, “wbrd”, “wcrd” through “wzrd”, can be checked, and so forth. Whenever a match is found within the dictionary, the spelling correction should be displayed to the screen.
For a detailed analysis how the other methods can be constructed, click here.
===== SIMPLE SPELL CHECKER =====
This program uses a custom template.h class. To obtain the code for that class, click here.
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// ============================================================================ // Author: Kenneth Perkins // Date: Jan 31, 2013 // Taken From: http://programmingnotes.org/ // File: SpellCheck.cpp // Description: This is a simple spell checker which tests the HashTable.h // class. // ============================================================================ #include <iostream> #include <fstream> #include <cctype> #include <cstring> #include <string> #include <iomanip> #include <ctime> #include <limits> #include "HashTable.h" using namespace std; // iterator declaration for hash table typedef HashTable<string>::Iterator iterDec; // hash table size const int TABLE_SIZE = 19000; // strtok delimiters const char* DELIMITERS = " ,.-\':;?()+*/\\%$#!\"@\^&"; // function prototypes void PrintTableStats(HashTable<string>& hashTable); int SpellCheck(HashTable<string>& hashTable, string word); string ToLowerCase(string word); int main() { // declare variables int result = 0; string userInput; string currWord; clock_t beg; // used to time the hashtable load clock_t end; // used to time the hashtable load char response; ifstream infile; HashTable<string> hashTable(TABLE_SIZE); // open the dictionary file infile.open("INPUT_Dictionary_programmingnotes_freeweq_com.txt"); // check if the file exists, EXIT if it doesnt if(infile.fail()) { cout<<"\n\n**ERROR - The dictionary file could not be found...\n"; exit(1); } cerr<<"\nLoading dictionary...."; beg = clock(); // start the timer // get data from file and put into hashtable while(infile >> currWord) { // makes sure duplicate words arent inserted into table if(!hashTable.Count(currWord)) { hashTable.Insert(currWord); } } infile.close(); PrintTableStats(hashTable); end = clock()-beg; // end the timer cout<<"\n\nDictionary loaded in "<< (double)end / ((double)CLOCKS_PER_SEC)<<" secs!"; // creates a line separator cout<<endl; cout.fill('-'); cout<<left<<setw(50)<<""<<endl; do{ // get user input cout<<"\n>> Please enter a sentence: "; getline(cin,userInput); cout<<endl; // split each word from the string into individual words to check if // they are spelled correctly char* splitInput = strtok(const_cast<char*>(userInput.c_str()),DELIMITERS); while(splitInput!=NULL) { currWord = splitInput; currWord = ToLowerCase(currWord); result += SpellCheck(hashTable,currWord); splitInput = strtok(NULL,DELIMITERS); } // display results if(result > 0) { cout<<"Number of words spelled incorrectly: "<<result<<endl; result = 0; } // ask for more data cout<<"\nDo you want to enter another sentence? (y/n): "; cin >> response; cin.ignore(numeric_limits<streamsize>::max(),'\n'); // clear the cin buffer }while(toupper(response)=='Y'); cout<<"\nBYE!!\n"; return 0; }// end of main void PrintTableStats(HashTable<string>& hashTable) { int largestBucket = -9999999; int largestIndex = 0; int smallestBucket = 9999999; int smallestIndex = 0; double numBuckestUsed = 0; ofstream outfile("OUTPUT_HashTable_Stats_programmingnotes_freeweq_com.txt"); for(int x=0; x < hashTable.TableSize(); ++x) { // iterator is used to traverse each hashtable bucket iterDec it = hashTable.begin(x); if(!hashTable.IsEmpty(x)) { if(smallestBucket > hashTable.BucketSize(x)) { smallestBucket = hashTable.BucketSize(x); smallestIndex = x; } if(largestBucket < hashTable.BucketSize(x)) { largestBucket = hashTable.BucketSize(x); largestIndex = x; } ++numBuckestUsed; outfile<<"\nBucket #"<<x<<":\n"; for(int y = 0; y < hashTable.BucketSize(x); ++y) { outfile <<"\t"<< it[y] << endl; } } } cout<<"Complete!\n"; // creates a line separator cout<<endl; cout.fill('-'); cout<<left<<setw(50)<<""<<endl; cout<<"Total dictionary words = "<<hashTable.TotalElems()<<endl <<"Hash table size = "<<hashTable.TableSize()<<endl <<"Largest bucket size = "<<largestBucket<< " items at index #"<<largestIndex<<endl <<"Smallest bucket size = "<<smallestBucket<< " items at index #"<<smallestIndex<<endl <<"Total buckets used = "<<numBuckestUsed<<endl <<"Total percent of hash table used = "<<(numBuckestUsed/hashTable.TableSize())*100<<"%"<<endl <<"Average bucket size = "<<(hashTable.TotalElems()/numBuckestUsed)<<" items"; }// end of PrintTableStats int SpellCheck(HashTable<string>& hashTable, string word) { int result = 0; int suggestion = 0; string remove[256]; int numRemove=0; if(!hashTable.Count(word)) { ++result; cout<<"** "<<word<<": "; // alteration & insertion for(unsigned x = 0; x < word.length(); ++x) { string alteration = word; for(char c = 'a'; c <= 'z'; ++c) { //alteration alteration[x] = c; if(hashTable.Count(alteration)) { cout<<alteration<<", "; remove[numRemove++] = alteration; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(alteration); } //insertion string insertion = word.substr(0, x) + c + word.substr(x); if(hashTable.Count(insertion)) { cout<<insertion<<", "; remove[numRemove++] = insertion; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(insertion); } } } // transposition & deletion for(unsigned x = 0; x < word.length()-1;++x) { // transposition string transposition = word.substr(0,x) + word[x+1] + word[x] + word.substr(x+2); if(hashTable.Count(transposition)) { cout<<transposition<<", "; remove[numRemove++] = transposition; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(transposition); } // deletion string deletion = word.substr(0, x)+ word.substr(x + 1); if(hashTable.Count(deletion)) { cout<<deletion<<", "; remove[numRemove++] = deletion; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(deletion); } } // place the removed items back inside the hash table while(numRemove>=0) { hashTable.Insert(remove[numRemove--]); } if(suggestion < 1) { cout<<"No spelling suggestion found..."; } cout<<endl<<endl; } return result; }// end of SpellCheck string ToLowerCase(string word) { for(unsigned x = 0; x < word.length(); ++x) { word[x] = tolower(word[x]); } return word; }// 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.
Remember to include the data file.
Once compiled, you should get this as your output
Loading dictionary....Complete!--------------------------------------------------
Total dictionary words = 61286
Hash table size = 19000
Largest bucket size = 13 items at index #1551
Smallest bucket size = 1 items at index #11
Total buckets used = 18217
Total percent of hash table used = 95.8789%
Average bucket size = 3.36422 itemsDictionary loaded in 1.861 secs!
-------------------------------------------------->> Please enter a sentence: wird
** wird: bird, gird, ward, weird, word, wild, wind, wire, wired, wiry,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: woprd
** woprd: word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: wrd
** wrd: ard, ord, ward, wed, word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: wrod
** wrod: brod, trod, wood, rod, word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: New! Safe and efective
** efective: defective, effective, elective,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: This is a sentance with no corections gygyuigigigiug
** sentance: sentence,
** corections: corrections,
** gygyuigigigiug: No spelling suggestion found...
Number of words spelled incorrectly: 3
Do you want to enter another sentence? (y/n): n
BYE!!
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 ===