## Java || Find The Prime, Perfect & All Known Divisors Of A Number Using A For, While & Do/While Loop

This program was designed to better understand how to use different loops which are available in Java, as well as more practice using objects with classes.

This program first asks the user to enter a non negative number. After it obtains a non negative integer from the user, the program determines if the user obtained number is a prime number or not, aswell as determining if the user obtained number is a perfect number or not. After it obtains its results, the program will display to the screen if the user inputted number is prime/perfect number or not. The program will also display a list of all the possible divisors of the user obtained number via stdout.

**REQUIRED KNOWLEDGE FOR THIS PROGRAM**

`Class Objects - How TO Use`

Constructors - What Are They?

Do/While Loop

While Loop

For Loop

Modulus

Basic Math - Prime Numbers

Basic Math - Perfect Numbers

Basic Math - Divisors

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import java.util.Scanner; public class PrimePerfectNums{ // global variable declaration int userInput = 0; static Scanner cin = new Scanner(System.in); public PrimePerfectNums(int input) {// this is the constructor // give the global variable a value userInput = input; }// end of PrimePerfectNums public void CalcPrimePerfect() { // declare variables int divisor = 0; int sumOfDivisors = 0; System.out.print("nInput number: " + userInput); // for loop adds sum of all possible divisors for(int counter=1; counter <= userInput; ++counter) { divisor = (userInput % counter); if(divisor == 0) { // this will repeatedly add the found divisors together sumOfDivisors += counter; } } System.out.println(""); // uses the 'sumOfDivisors' variable from ^ above for loop to // check if 'userInput' is prime if(userInput == (sumOfDivisors - 1)) { System.out.print(userInput + " is a prime number."); } else { System.out.print(userInput + " is not a prime number."); } System.out.println(""); // uses the 'sumOfDivisors' variable from ^ above for loop to // check if 'userInput' is a perfect number if (userInput == (sumOfDivisors - userInput)) { System.out.print(userInput + " is a perfect number."); } else { System.out.print(userInput + " is not a perfect number."); } System.out.print("nDivisors of " + userInput + " are: "); // for loop lists all the possible divisors for the // 'userInput' variable by using the modulus operator for(int counter=1; counter <= userInput; ++counter) { divisor = (userInput % counter); if(divisor == 0 && counter !=userInput) { System.out.print(counter + ", "); } } System.out.print("and " + userInput); }// end of CalcPrimePerfect public static void main(String[] args) { // declare variables int input = 0; char response ='n'; do{ // this is the start of the do/while loop System.out.print("Enter a number: "); input = cin.nextInt(); // if the user inputs a negative number, do this code while(input < 0) { System.out.print("ntSorry, but the number entered is less " + "than the allowable limit.ntPlease try again....."); System.out.print("nnEnter an number: "); input = cin.nextInt(); } // entry point to class declaration PrimePerfectNums myClass = new PrimePerfectNums(input); // function call to obtain data using the number // which was passed from main to the constructor myClass.CalcPrimePerfect(); // asks user if they want to enter new data System.out.print("nntDo you want to input another number?(Y/N): "); response = cin.next().toLowerCase().charAt(0); System.out.println("---------------------------" + "---------------------------------"); }while(response =='y'); // ^ End of the do/while loop. As long as the user chooses // 'Y' the loop will keep going. // It stops when the user chooses the letter 'N' System.out.println("BYE!"); }// 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:

`Enter a number: 41`

Input number: 41

41 is a prime number.

41 is not a perfect number.

Divisors of 41 are: 1, and 41Do you want to input another number?(Y/N): y

------------------------------------------------------------

Enter a number: 496Input number: 496

496 is not a prime number.

496 is a perfect number.

Divisors of 496 are: 1, 2, 4, 8, 16, 31, 62, 124, 248, and 496Do you want to input another number?(Y/N): y

------------------------------------------------------------

Enter a number: 1858Input number: 1858

1858 is not a prime number.

1858 is not a perfect number.

Divisors of 1858 are: 1, 2, 929, and 1858Do you want to input another number?(Y/N): y

------------------------------------------------------------

Enter a number: -9Sorry, but the number entered is less than the allowable limit.

Please try again.....Enter an number: 12

Input number: 12

12 is not a prime number.

12 is not a perfect number.

Divisors of 12 are: 1, 2, 3, 4, 6, and 12

`Do you want to input another number?(Y/N): n`

------------------------------------------------------------

BYE!

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