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

static long num_steps = 100000000;

int main ()
{
	int j;
	double pi, sum = 0.0;

	double step = 1.0/(double) num_steps;

	int P = omp_get_max_threads();	// available treads
	double *sums = (double*) malloc(P*sizeof(double));

	#pragma omp parallel
	  {
		int i;
		double x;
		double psum = 0.0; // private
		int ID = omp_get_thread_num();
		for (i=ID;i< num_steps; i = i+P){
			x = (i+0.5)*step;
			psum = psum + 4.0/(1.0+x*x);

		}
		sums[ID] = psum;
	  }

	for (j = 0; j < P; j++)
		sum += sums[j];
	pi = step * sum;

	printf("pi=%lf\n", pi);

	free(sums);

}