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

int main(argc, argv)
int argc;
char *argv[];
 {
  int n, myid, numprocs, i;
  double PI25DT = 3.141592653589793238462643;
  double mypi, pi, h, sum, x;
  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD,&myid);
  while(1)
   {
    if (myid == 0)
     {
      printf("Enter the number of intervals: (0 quits) \n");
      fflush(stdout);
      scanf("%d",&n);
     } // if myid == 0
    MPI_Bcast(&n,1,MPI_INT,0,MPI_COMM_WORLD);
    if (n == 0) break;
    else
     {
      h = 1.0 / (double) n;
      sum = 0.0;
      for (i = myid + 1; i <= n; i+= numprocs)
       {
        x = h * ((double)i - 0.5);
        sum += (4.0 / (1.0 + x*x));
       } // for
      mypi = h * sum;
      MPI_Reduce(&mypi,&pi,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
      if (myid == 0) 
       printf("pi is approximately %.16f, Error is %.16f\n", 
        pi, fabs(pi - PI25DT));
     } // else 
   } // while(1)
  MPI_Finalize();
  return 0;
 } // main