/* This program computes the value of PI */

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

int main(int argc, char *argv[])
{
  int done = 0, n, myid, numprocs, i, rc;
  double PI25DT = 3.141592653589793238462643;
  double mypi, pi, h, sum, sum1, x, a;
  int fds[2];

  if (argc != 2) {
    printf("Usage: a.out N\n");
    exit(0);
  }
  n = atoi(argv[1]);

  pipe(fds);

  if (fork() == 0) {
    h   = 1.0 / (double) n;
    sum = 0.0;

    for (i = n/2; i <= n; i ++) {
      x = h * ((double)i - 0.5);
      sum += 4.0 / (1.0 + x*x);
    }
    write(fds[1], &sum, sizeof(sum));
    exit(0);
  }

  h   = 1.0 / (double) n;
  sum = 0.0;

  for (i = 1; i < n/2; i ++) {
    x = h * ((double)i - 0.5);
    sum += 4.0 / (1.0 + x*x);
  }
  read(fds[0], &sum1, sizeof(sum));
  mypi = h * (sum+sum1);
  printf("pi is approximately %.16f, Error is %.16f\n", mypi, fabs(mypi - PI25DT));
  return 0;
}