omp_pi.c

#include <omp.h>
#include <stdlib.h>
#include <stdio.h>
#define SEED 35791246

int main(int argc, char* argv[])
{
    printf("Enter the number of iterations used to estimate pi:\n");
    fflush(stdout);
    int niter=0;
    double x,y;
    int i,tid,count=0; /* # of points in the 1st quadrant of unit circle */
    double z;
    double pi;
    scanf("%d",&niter);
#pragma omp parallel for private(x,y,z,tid) reduction(+:count)
    for ( i=0; i<niter; i++) {
        if (i==0)srand(SEED+omp_get_thread_num()*234);
        //if(i==0)    printf("the thread count is %i\n",omp_get_num_threads( ));
        x = (double)rand()/RAND_MAX;
        y = (double)rand()/RAND_MAX;
        z = (x*x+y*y);
        if (z<=1) count++;
    }
    printf(" the total count is %i\n",count);
    pi=(((double)count)/niter)*4;
    printf("# of trials= %d , estimate of pi is %g \n",niter,pi);
    return 0;

}

Two Runs