Program in C to check the number is prime or not.

Solution:

As per the definition, a positive integer which is only divisible by 1 and itself is known as prime number. 

For example: 

Let, 13 is a prime number because it is only divisible by 1 and 13 but, 15 is not prime number because it is divisible by 1, 3, 5 and 15.

Program:

#include <stdio.h>

#include<conio.h>

int main()

{

int n, i, flag=0;

printf("\n Enter a positive integer: ");

  scanf("%d", &n);

  for(i=2;i<=n/2;++i)

  {

if(n%i == 0)

      {

      flag=1;

         break;

}

  }

  if (flag == 0)

      printf("\n %d is a prime number",n);

  else

      printf("\n %d is not a prime number",n);

  return (0);

}

Output 1:

Enter a positive integer: 17

17 is not a prime number

Output 2:

Enter a positive integer: 21

21 is a prime number