/* prime.c - print prime numbers up to 1000
 * To compile this program, type:  gcc -o prime prime.c
 *   Or you can put the "-o prime" after the "prime.c"
 */
#include <stdio.h>
#define YES 1
#define NO  0

/* For a number to be prime, there must be exactly one factor in the
 * range from 1 up to and including the square root of n.  In other words,
 * from 2 to the sqrt(n), there cannot be any factors.
 */
int is_prime(int n)
{
  int i;
  
  // Special case
  if (n == 1)
    return NO;

  for (i = 2; i*i <= n; ++i)
    if (n % i == 0)
      return NO;

  // If we get this far, we didn't find a divisor.  That's good!
  return YES;
}

main()
{
  int candidate, num_primes = 0;

  // We know the first prime number is 2.
  for (candidate = 2; candidate <= 1000; ++candidate)
    if (is_prime(candidate))
    {
      printf("%d\n", candidate);
      ++ num_primes;
    }

  printf("I found %d prime numbers.\n", num_primes);
}