mpi_relay

#include <stdio.h>
#include <string.h>
#include <mpi.h>
#define arr_size 20

int main (int argc, char **argv)
{
    char message[arr_size] = {};
    int rank, size;

    strcpy(message, "Hi, process");

    MPI_Status status;
    MPI_Init (&argc, &argv);
    MPI_Comm_rank (MPI_COMM_WORLD, &rank);
    MPI_Comm_size (MPI_COMM_WORLD, &size);

    if ( (rank+1) < size)
    {
        MPI_Send(message, strlen(message), MPI_CHAR, rank+1, 99, MPI_COMM_WORLD);
        printf("I'm %d. Sent msg to %d\n", rank, rank+1);

        MPI_Recv(message, strlen(message), MPI_CHAR, rank-1, 99, MPI_COMM_WORLD, &status);
        if (rank != 0)
            printf("I'm %d. Received msg from %d\n", rank, rank-1);
        else
            printf("I'm %d. Received msg from %d\n", rank, size-1);

    }
    else
    {
        MPI_Send(message, strlen(message), MPI_CHAR, 0, 99, MPI_COMM_WORLD);
        printf("I'm %d. Sent msg to %d\n", rank, 0);

        MPI_Recv(message, strlen(message), MPI_CHAR, rank-1, 99, MPI_COMM_WORLD, &status);
        printf("I'm %d. Received msg from %d\n", rank, rank-1);
    }
    MPI_Finalize();

    return 0;
}