enum class MachineState {
    Startup,
    Ready,
    PendigPayment,
    Release,
    Unlock,
    Shutdown
}

// SIMULATING HARDWARE-REQUESTS

int main() {
    MachineState state = MachineState.Startup;
    while(true) {
        state = MachineState.Ready;

        std::string = std::cin << "Pick your slot" << std::endl;
    }
    return 0;
}