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

/*
 * The program sends an integer to a slave process. The slave
 * increases the value by one and then sends it back.
 * The program should be used with two processes.
 */

int main(int argc, char *argv[])
{
  int message, length, source, dest, tag;
  int my_rank;
  int n_procs;                  /* number of processes */
  MPI_Status status;


  MPI_Init(&argc, &argv);       /* Start up MPI */

  /* Find out the number of n_processes and my rank */
  MPI_Comm_size(MPI_COMM_WORLD, &n_procs);
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

  tag = 1;
  length = 1;                   /* Length of message */

  if (my_rank == 0) {           /* I'm the master process */
    printf("Number of processes = %d\n", n_procs);
    dest = 1;                   /* Send to the other process */
    message = 1;                /* Just send one int */

    /* Send message to slave */
    MPI_Send(&message, length, MPI_INT, dest, tag, MPI_COMM_WORLD);
    printf("After MPI_Send\n");

    source = 1;
    /* Receive message from slave */
    MPI_Recv(&message, length, MPI_INT, source, tag, MPI_COMM_WORLD,
             &status);

    printf("After MPI_Recv, message = %d\n", message);

  } else {                      /* I'm the slave process */

    source = 0;
    /* Receive message from master */
    MPI_Recv(&message, length, MPI_INT, source, tag, MPI_COMM_WORLD,
             &status);
    dest = 0;                   /* Send to the other process */
    message++;                  /* Increase message */
    /* Send message to master */
    MPI_Send(&message, length, MPI_INT, dest, tag, MPI_COMM_WORLD);
  }

  MPI_Finalize();               /* Shut down MPI */

  return 0;
}