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A whole number greater than 1 that cannot be exactly divided by any whole number other than itself and 1 is called a prime number.

For Example:

3, 5, 7 , 13 … are prime numbers because they can only divide by 1 or the number itself.

Required Knowledge

• C Programming Basics
• C Programming Operators
• C printf and Scanf
• While loop in C

Steps to writing prime number program in java

• Here we are using “Scanner” to take input for numbers.
• We will start the loop from 2 as 1 is not a prime number and limit it to number/2 as it will be useless iterations.
• Inside the loop, we are checking the divisibility of the number with i starting from 2. If it is divisible then we break from the loop as it definitely is not a prime number because it is fully divisible by other numbers as well.
• Else we keep on iterating till number/2.

Prime number program in Java

import java.util.*;
public class Main
{
	public static void main(String args[])
	{
		System.out.println("Prime Number program in Java While loop ");
		Scanner sc = new Scanner(System.in);				
		int i = 2;
		boolean flag = false;		
		System.out.println("Enter the Number to check for prime : ");
		int number = sc.nextInt();		
		while(i<=number/2) {			
			if(number%i == 0) {
				flag = true;
				break;
			}
			++i;
		}		
		if (!flag)
		      System.out.println(number + " is a prime number.");
		    else
		      System.out.println(number + " is not a prime number.");
		sc.close();
	}	  
}

Output 1:

Prime Number program in Java While loop 
Enter the Number to check for prime: 
31
31 is a prime number.

Output 2:

Prime Number program in Java While loop 
Enter the Number to check for prime : 
12
12 is not a prime number.