//// bad
int number;
if (world_rank == 0) {
    number = -1;
    MPI_Bcast(&number, 1, MPI_INT, 0, MPI_COMM_WORLD);
} else {
    MPI_Recv(&number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD,MPI_STATUS_IGNORE);
}