JAVA program to check whether a given number is prime or not

This JAVA program is to check whether a given number is a prime number or not.

For example 11 is a prime number and 8 is not a prime number.

Logic

We are using the logic of prime number which is – a prime number is divisible by 1 and number itself.

So the count should be 2.If it is greater than 2 than we know that it is also divisible by another number so it then becomes a composite number.

Dry Run of the Program

Take input as integer variable ‘n’ .Let us take n=4

1st iteration   for(i=1;i<= n;i++)  i.e. for(i=1;i<=3;i++)

if (n%i==0)  i.e if(3%1==0)  this condition is true

So c is incremented  , hence c++; i.e. c=1;

2nd iteration   for(i=2;i<= n;i++)  i.e. for(i=2;i<=3;i++)

if (n%i==0)  i.e if(3%2==0)  this condition is false so c is not incremented

3rd iteration   for(i=3;i<= n;i++)  i.e. for(i=3;i<=3;i++)

if (n%i==0)  i.e if(3%3==0)  this condition is true so c is incremented

So c++; hence c=2;

For loop ends here as now when i is incremented i=4 hence i>n

Now we check the condition if(c==2)

As c=2 is true we print 3 is a prime no.

Program

import java.util.*;

class prime {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the no");
        int n = sc.nextInt();
        int i=1,c=0;
	for(i=1;i<=n;i++)	
	{            
		if(n%i==0)
		{
			c++;
		}		      
	}
	
	if(c==2)
	{
 		System.out.println(n+" is a PRIME no");
	}
	else
	{
 		System.out.println(n+" is a NOT a prime no");
	}
    }
}

Output