#include "mpi.h"

 #include <stdio.h>

 #include <stdlib.h>

 #include <time.h>

 #include <string.h>

 #include <iostream>

 #include <unistd.h>

 using namespace std;

 int main(int argc, char **argv)

 {

     int myid, numprocs, num;

     MPI_Init(&argc, &argv);

     MPI_Comm_rank(MPI_COMM_WORLD, &myid);

     MPI_Comm_size(MPI_COMM_WORLD, &numprocs);

     MPI_Status status;

     if (numprocs < ) {

         printf("Processes must >= 2! \n");

         MPI_Abort(MPI_COMM_WORLD, );

     }

     do {

         //master

         if (myid == ) {

             cout << "please input a number" << endl;

             cin >> num;

             //send number

             if (numprocs > ) {

                 MPI_Send(&num, , MPI_INT, myid + , , MPI_COMM_WORLD);

                 cout << myid << " send " << num << " to " << myid +  << endl;

             }

         }

         //slave

         else {

             MPI_Recv(&num, , MPI_INT, myid - , , MPI_COMM_WORLD, &status);

             cout << myid << " receive " << num << " from " << myid -  << endl;

             if (myid < numprocs - ) {

                 MPI_Send(&num, , MPI_INT, myid + , , MPI_COMM_WORLD);

                 cout << myid << " send " << num << " to " << myid +  << endl;

             }

         }

         MPI_Barrier(MPI_COMM_WORLD); // wait all pro finish

     } while (num > );

     MPI_Finalize();

     return ;

 }