C > Miscellaneous

Test for primes

Test for primes

#include <stdio.h>
#include <getopt.h>
#include <stdlib.h>

int isprime(int value);

int main(int argc, char *argv[]) {
 int number = 0; 

 if(argc != 2) {
  fprintf(stderr, "Usage: isprime INT\n");
  return 1;
 } else
  number = atoi(argv[1]);

 if(isprime(number) == 0)
  printf("%2d is NO prime\n", number);
 else
  printf("%2d is a prime...\n", number);

 return 0;
}

int isprime(int value) {
 int retval = -1;
 int i = 0;

 for(i = 2; i <= value / 2; i++) {
  if(value % i == 0) {
   retval = 0;
   break;
  }
 }

 return retval;
}