c++ - 如何让定时器在后台保持运行

Question

我正在为我的俱乐部编写程序。要求用户在 2 分钟内回答 10 个问题。我正在为每个问题使用函数，并在用户回答完当前问题后调用下一个函数。如何在显示问题的同时在顶部显示剩余时间？

我试过循环来控制我的时间。但它不会在顶部显示剩余时间并同时显示问题，因为循环需要执行直到条件为假

Question1()
{
countdown();
cout<<"Question 1 out of 10"<<endl<<endl;
cout<<" Where Is The First Indoor Bowling Lane Built? "<<endl;
cout<<"A. New York City"<<endl;
cout<<"B. Berlin"<<endl;
cout<<"C. Ohio"<<endl;
cout<<"D. Japan"<<endl;
cout<<"Your answer: ";                                                                                                                       
cin>>ans1;
Question2();
}
void countdown()
{
while(timer>=0)
{
cout<<"Time remaining: "<<timer<<endl;
Sleep(1000);
timer--;
system("cls");
}
}

预计时间会在我的问题上进行倒计时，但问题只会在设定的时间结束前显示。

Answer 1

我回想起 MS-DOS 的日子，记得有一个函数 _kbhit由 <conio.h> 提供在 Windows 中。它不是可移植的，但也许你不在乎。这是我编写的一个函数，将使用 _kbhit轮询按键。它很粗糙，但也许这就是您要找的东西。

int GetInputWithTimeout(int count, int timeout)
{
    int answer = -1;
    const int poll_rate = 10;
    int poll_cycle = 0, last_timeout = 0;
    do {
        // poll for keypress and store answer if valid
        if (_kbhit())
        {
            int input = _getch();
            while (_kbhit()) _getch(); // discard control sequences
            input = tolower(input);
            if (input >= 'a' && input < 'a' + count)
            {
                answer = input - 'a';
            }
        }

        // display time remaining if changed
        if (last_timeout != timeout) {
            last_timeout = timeout;
            std::cout << "\rTime remaining: " << timeout << " " << std::flush;
        }

        // perform small sleeps for a potentially wildly inaccurate, but responsive delay
        if (timeout > 0)
        {
            Sleep(1000 / poll_rate);
            poll_cycle = (poll_cycle + 1) % poll_rate;
            if (poll_cycle == 0) --timeout;
        }
    } while (timeout > 0 && answer == -1);
    std::cout << std::endl;
    return answer;
}

因此您可以使用此函数，传递所需数量的测验输入。建议的用法是这样的:

struct Question {
    std::string question;
    std::vector<std::string> answers;
    int correct_answer;
    int timeout_seconds = 10;
};

bool AskQuestion(int number, const Question& question)
{
    std::cout << "Question " << number << ": " << question.question << std::endl;
    int count = static_cast<int>(question.answers.size());
    for (int i = 0; i < count; i++)
    {
        std::cout << "  " << char('A' + i) << ": " << question.answers[i] << std::endl;
    }
    int answer = GetInputWithTimeout(count, question.timeout_seconds);
    return answer == question.correct_answer;
}

您会注意到我在结构中表示了一个测验问题。因此，您可以像这样设置和运行整个测验:

int main()
{
    std::vector<Question> questions = {
        {
            "Where Is The First Indoor Bowling Lane Built?",
            {
                "New York City",
                "Berlin",
                "Ohio",
                "Japan"
            },
            0, // I have no idea, so just guessed it's new york
        },
        {
            "What is the airspeed velocity of an unladen swallow?",
            {
                "10km/h",
                "20km/h",
                "30km/h",
                "40km/h",
                "What do you mean -- an african or european swallow?"
            },
            4,
        },
    };

    int num_questions = static_cast<int>(questions.size());
    int num_correct = 0;    
    for (int q = 0; q < num_questions; q++)
    {
        num_correct += AskQuestion(q, questions[q]);
        std::cout << std::endl;
    }

    std::cout << "Final score: " << num_correct << " of " << num_questions << std::endl;
    return 0;
}

呃，糟糕，我有点为你写了整个程序。它并不漂亮，但希望它至少能教给你一些东西。