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C Program to Check Whether a Number is Prime or Not

C Program to Check Whether a Number is Prime or Not

A prime number is a positive integer which is divisible only by 1 and itself. For example: 2, 3, 5, 7, 11, 13

#include <stdio.h>
int main()
{
    int n, i, flag = 0;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=2; i<=n/2; ++i)
    {
        // condition for nonprime number
        if(n%i==0)
        {
            flag=1;
            break;
        }
    }

    if (flag==0)
        printf("%d is a prime number.",n);
    else
        printf("%d is not a prime number.",n);
    
    return 0;
}

If the for loop terminates when the test expression of loop i <= n/2 is false, the entered number is a prime number. The value of flag is equal to 0 in this case.

If the loop terminates because of break statement inside the if statement, the entered number is a nonprime number. The value of flag is 1 in this case.

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