static int kbhit(void){
    struct timeval timeout;
    fd_set read_handles;
    int status;

    // check stdin (fd 0) for activity
    FD_ZERO(&read_handles);
    FD_SET(0, &read_handles);
    timeout.tv_sec = timeout.tv_usec = 0;
    status = select(0 + 1, &read_handles, NULL, NULL, &timeout);
    return status;
}