/* Calculates number of primes between 1 and 20 million.
 * CS 226 Lab 6  */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>
#include <pthread.h>

//returns whether num is prime
bool isPrime(long num) {
  int limit = (int) sqrt(num);
  for(long i=2; i<=limit; i++) {
    if(num % i == 0)
      return false;
  }
  return true;
}

// start should be odd.
void count_primes (long *pCount, long start, long finish)
{
  while(start < finish) {
    if(isPrime(start)) {
      ++*pCount;
    }
    start += 2;
  }
}

int main () {
  long pCount = 1;   //(starting with 2)

  count_primes (&pCount, 3, 20000000);

  printf ("%ld primes found", pCount);
}