Program that checks whether a number is prime or not using a for loop:

    #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++)
    {
      if(n % i == 0)
     {
         flag = 1;
         break;
     }
   }
   if (n == 1)
   {
      printf("1 is neither prime nor composite.\n");
   }
   else
   {
      if (flag == 0)
         printf("%d is a prime number.\n", n);
      else
         printf("%d is not a prime number.\n", n);
   }

   return 0;
   }

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