prime.c

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

#define FALSE 0
#define TRUE 1


int isPrime(int num) {
  if (num == 0) {
    return FALSE;
  }
  if (num == 1) {
    return FALSE;
  }
  if (num == 2) {
    return TRUE;
  }
  int i;
  for (i = 3; i < num - 1; i += 2) {
    //printf("loop %i in %i ", num, i);
    if (num % i == 0) {
      return FALSE;
    }
  }

  return TRUE;
}


int main(void){
  int targets[100] = {0};

  int i;
  for (i = 0; i < 100; i++) {
    char temp[10];
    fgets(temp, 10, stdin);
    int result = atoi(temp);
    if (result == 0) {
      break;
    }
    targets[i] = result;
  }

  int checkCount;
  for (checkCount = 0; checkCount < 100; checkCount++) {
    if (targets[checkCount] == 0)
      break;

    int result = 0;
    if (targets[checkCount] > 2)
      result++;

    int i;
    for(i = 3; i < targets[checkCount]; i += 2){
      int prime = isPrime(i);
      if (prime == TRUE) {
        //printf("%i,", i);
        result++;
      }
    }
    printf("%i\n", result);
  }
  return 0;
}