#include "stdafx.h"
#ifdef _OPENMP 
  #include <omp.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>


void PI(double a, double b, int numIntervals, double* global_result_p) {
   int i;
   double x, my_result, sum = 0.0, interval, local_a, local_b, local_numIntervals;
   int myThread = omp_get_thread_num();
   int numThreads = omp_get_num_threads();
  
   interval = (b-a)/ (double) numIntervals;
   local_numIntervals = numIntervals/numThreads; 
   local_a = a + myThread*local_numIntervals*interval; 
   local_b = local_a + local_numIntervals*interval; 
   sum = 0.0;
   for (i = 0; i < local_numIntervals; i++) {
      x = local_a + i*interval;
      sum = sum + 4.0 / (1.0 + x*x);
   };
   my_result = interval * sum;

   #  pragma om critical 
   *global_result_p += my_result; 
}

int main(int argc, char* argv[]) {
   double   global_result = 0.0;
   volatile DWORD dwStart;

   int n = 100000000;
      printf("numberInterval %d \n", n);
   int numThreads = strtol(argv[1], NULL, 10);
   dwStart = GetTickCount();
   #  pragma omp parallel num_threads(numThreads) 
      PI(0, 1, n, &global_result); 

   printf("number of threads %d \n", numThreads);
   printf("Pi = %f \n", global_result);
   printf_s("milliseconds %d \n", GetTickCount() - dwStart);
}