#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// MPI include file 

int main( int argc, char *argv[])
/*
!   piArea.f90 - compute pi by counting random points in circle and
!                  circumscribing square.
!                The circle has centre in the origin and radius 1
!
!
!   Each process:
!    1) receives the number of rectangles used in the approximation
!    2) generates and count points in rectangle and circle
!    3) Synchronizes for a global summation.
!   Process 0 prints the result.
!
!  Variables:
!
!    pi          the calculated result
!    n           number of random points 
!    x1, x2      extremes of each rectangle
!    SqPoints    points in each rectangle
!    CiPoints    points in circle      
!
*/
{
    int done = 0, n, myid, numprocs, i;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h;
    double x, y, x1, x2, y1, y2;
    int SqPoints, CiPoints, my_SqPoints, my_CiPoints;
    double startwtime = 0.0, endwtime;
    int  namelen;

    // MPI initialization: define numprocs and myid
    
    numprocs = 1; myid = 0;

    fprintf(stderr,"Process %d alive\n",myid);

    n = 0;
    while (!done)
    {
        
        if (myid == 0)
        {
            printf("Enter the number of points: (0 quits) \n");
            scanf("%d",&n);

        }
        // Send number of points to all processes
        if (n <= 0)
            done = 1;
        else
        {
            h   = 2.0 / (double) numprocs;
            x1 = -1.0 + myid * h;
            x2 = x1 + h;
            y1 = -1.0;
            y2 = 1.0;
            my_SqPoints  = 0;
            my_CiPoints  = 0;

            for (i = 1; i <= n; i += numprocs)
            {
                x = rand(); x = x / RAND_MAX; x = x1 + x * (x2 - x1);
                y = rand(); y = y / RAND_MAX; y = y1 + y * (y2 - y1);
                my_SqPoints++;
                if ( sqrt( x*x + y*y ) <= 1.0 ) my_CiPoints++;
            }

            // Sum up SqPoints from all processes: result in SqPoints
            // Sum up CiPoints from all processes: result in CiPoints
            SqPoints = my_SqPoints;
            CiPoints = my_CiPoints;

            if (myid == 0)
            {
                pi = 4.0 * (double)CiPoints / (double)SqPoints;
                printf("pi is approximately %.16f, Error is %.16f\n",
                       pi, fabs(pi - PI25DT));
            }
        }
    }
    // MPI finalization

    return 0;
}