ACM International Collegiate Programming Contest, Japan Domestic, 2006, Problem A

gistfile1.c

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

#define TRUE 1
#define FALSE 0

int main(int argc, char *argv[])
{
  FILE *in;
  int a, d, n;
  int number;

  if (argc != 2) {
    fprintf(stderr, "usage: %s file\n", argv[0]);
    exit(1);
  }

  if ((in = fopen(argv[1], "r")) == NULL) {
    fprintf(stderr, "cannot open %s\n", argv[0]);
  }

  while (1) {
    fscanf(in, "%d %d %d", &a, &d, &n);
    if (a == 0 && d == 0 && n == 0) {
      break;
    }
    number = a;
    while (n != 0) {
      if (isPrime(number) == TRUE) {
        if (n == 1) {
          printf("%d\n", number);
          break;
        }
        n --;
      }
      number += d;
    }
  }
}

int isPrime(int x)
{
  int i;

  if (x == 1) {
    return FALSE;
  }
  for (i = 2; i < x; i ++) {
    if (x % i == 0) {
      return FALSE;
    }
  }
  return TRUE;
}