char *message;
message= (char*)malloc(msg_size);

int main(int argc, char **argv)
    {

    double startwtime, endwtime;
    float  elapsed_time, bandwidth;

    int my_id, next_id; /* process id-s */
    int p;      /* number of processes */
    char* message;  /* storage for the message */
    int i, k, max_msgs, msg_size, v;
    MPI_Status status;  /* return status for receive */


    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &my_id );
    MPI_Comm_size( MPI_COMM_WORLD, &p );

    if (argc < 3)
    {
    fprintf (stderr, "need msg count and msg size as paramsn");
    goto EXIT;
    }

    if ((sscanf (argv[1], "%d", &max_msgs) < 1) ||
                (sscanf (argv[2], "%d", &msg_size) < 1))
    {
    fprintf (stderr, "need msg count and msg size as paramsn");
    goto EXIT;
    }

    **message = (char*)malloc (msg_size);**
    if (argc > 3) v=1; else v=0;           /*are we in verbose mode*/

    /* don't start timer until everybody is ok */
    MPI_Barrier(MPI_COMM_WORLD);
int t=0;
    if( my_id == 0 ) {
    startwtime = MPI_Wtime();

        // do max_msgs times:
        //   send message of size msg_size chars to process 1
        //   receive message of size msg_size chars from process p-1
while(t<max_msgs) {
MPI_Send((char *) message, msg_size, MPI_CHAR, 1 , 0, MPI_COMM_WORLD);
MPI_Recv((char *) message, msg_size, MPI_CHAR, p-1, 0, MPI_COMM_WORLD, &status);
t++;
}
        MPI_Barrier(MPI_COMM_WORLD);
    endwtime = MPI_Wtime();
    elapsed_time = endwtime-startwtime;
    bandwidth = 2.0 * max_msgs * msg_size / (elapsed_time);
        printf("Number, size of messages: %3d , %3d n", max_msgs, msg_size);
        fflush(stdout);
        printf("Wallclock time     = %f secondsn", elapsed_time );
        fflush(stdout);
        printf("Bandwidth          = %f bytes per secondn", bandwidth);
        fflush(stdout);
    } else if( my_id == p-1 ) {

        // do max_msgs times:
        //   receive message of size msg_size from process to the left
        //   send message of size msg_size to process to the right (p-1 sends to 0)
    while(t<max_msgs) {
        MPI_Send((char *) message, msg_size, MPI_CHAR, 0, 0, MPI_COMM_WORLD);
        MPI_Recv((char *) message, msg_size, MPI_CHAR, my_id-1, 0, MPI_COMM_WORLD, &status);
        t++;
    }
    } else {
        while(t<max_msgs) {
        MPI_Send((char *) message, msg_size, MPI_CHAR, my_id+1, 0, MPI_COMM_WORLD);
        MPI_Recv((char *) message, msg_size, MPI_CHAR, my_id-1, 0, MPI_COMM_WORLD, &status);
        t++;
        }
          }

      MPI_Barrier(MPI_COMM_WORLD);

EXIT:
    MPI_Finalize();
    return 0;
}