A Program to Check a Prime Number

In this example, we are giving a program to check whether a number is prime or not. A number can be said prime if the number is divisible only by 1 and itself. For example: 2, 3, 5, 7, 11, 13, 17, 19 etc.


Program to check prime:

  1. #include <stdio.h>
  2. int main() {
  3. int n, i, flag = 0;
  4. printf("Enter a positive integer: ");
  5. scanf("%d", &n);
  6. for (i = 2; i < n / 2; ++i) {
  7. // condition for non prime number
  8. if (n % i == 0) {
  9. flag = 1;
  10. break;
  11. }
  12. }
  13. if (n == 1) {
  14. printf("1 is neither prime nor composite.");
  15. }
  16. else {
  17. if (flag == 0)
  18. printf("%d is a prime number.", n);
  19. else
  20. printf("%d is not a prime number.", n);
  21. }
  22. return 0;
  23. }

Output:

Enter a positive integer: 7
7 is a prime number.