pi3par.c

#include <omp.h>
#include <math.h>
#include <stdio.h>
 
int main(argc,argv)
int argc;
char *argv[];
{
    int done = 0, n, tid, numprocs, i, len;
    double PI25DT = 3.141592653589793238462643;
    double pi, h, sum, x;
    

    while (!done)
    {
            printf("Enter the number of intervals: (0 quits) ");
            scanf("%d",&n);
            
            if (n == 0) break;
         
        h   = 1.0 / (double) n;
        sum = 0.0;

#pragma omp parallel private(i,x,tid,numprocs) default(shared) reduction(+:sum)
    {    
        tid = omp_get_thread_num();
        numprocs= omp_get_num_threads();

        for (i = 1 + tid ; i <= n; i+= numprocs) {
        printf("%d: %d\n",tid,i);
            x = h * ((double)i - 0.5);
            sum += 4.0 / (1.0 + x*x);
        }

    }
        pi = h * sum;

        printf("pi is approximately %.16f, Error is %.16f\n",
                pi, fabs(pi - PI25DT));
    }
    return 0;
}