/* File: primes1.c
   Single thread version to see how slow 

   compile with: g++ primes1.c -o primes1
   to get timing, run with: time ./primes1

*/

#include <stdio.h>
#include <math.h>


// deliberately slow algorithm for checking primality
//
int isPrime (unsigned int n) {
   unsigned int m = sqrt(n) ;

   for (unsigned int k=2 ; k <= m ; k++) {
      if (n % k == 0) return 0 ;
   }
   return 1 ;
}


int main() {

   int numPrimes=0 ;
   const int n=10000000 ;  // 10 million

   for(int i=2 ; i < n ; i++) {
      if ( isPrime(i) )  numPrimes++  ;
   }

   printf("Number of primes less than %d is %d\n", n, numPrimes) ;


   return 0 ;
}