int number;
MPI_Status status;
MPI_Request in_request = MPI_REQUEST_NULL;
if (world_rank == 0) {
    number = -1;
    MPI_ISend(&number, 1, MPI_INT, 1, 0, MPI_COMM_WORLD, &request);
} else if (world_rank == 1) {
    MPI_IRecv(&number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE, &request);
    printf("Process 1 received number %d from process 0\n", number);
}

MPI_Wait(&request, &status);