Question

在我的代码中，while循环打印cout两次，它应该打印一次，以及函数的couts。我不明白为什么要这样做 - 它应该显示

你想做什么？

存款

退出

取消

但是，它会显示两次。

while (yesNo == 'Y') {

        cout << "What would you like to do?"
            << endl
            << endl;

        menu();
        getline(cin, bankChoice);

        if (bankChoice == "Withdraw")
        {

            withdrawTotal = withdraw(bankAmount);
            bankAmount = withdrawTotal;
            cout << "You now have $"
                << bankAmount
                << " in your account."
                << endl;

            cout << "Would you like to do anything else?"
                << endl
                << "Y/N: ";
            cin >> yesNo;

        }

        if (bankChoice == "Deposit")
        {

            depositTotal = deposit(bankAmount);
            bankAmount = depositTotal;
            cout << "You now have $"
                << bankAmount
                << " in your account."
                << endl;

            cout << "Would you like to do anything else?"
                << endl
                << "Y/N: ";
            cin >> yesNo;
        }


        if (bankChoice == "Cancel") {
            return 0;
        }

    }

这就是我正在使用的循环。如果需要额外的代码，我也可以发布它，但这是造成问题的部分。我已经尝试了没有它的代码并且工作正常，但是我想让代码循环直到用户输入N＆＃39;。

Answer 1

您正在使用std::getline和operator>>来阅读std::cin。 operator>>不使用尾随换行符，因此下一次调用std::getline（）将立即读取以下换行符并将其解释为输入的空行文本。这将贯穿循环，并返回到顶部，以进行第二次提示。

当您打算阅读一行文字时，切勿将operator>>与std::cin一起使用。

以下简短示例说明了这一点：

#include <iostream>
#include <string>

int main()
{
    char c;
    std::string l;

    std::cin >> c;

    std::cout << "A line of text please: ";

    std::getline(std::cin, l);
}

运行它，输入“Y”，并尝试自己解决，为什么程序会立即终止。

再次：不要使用operator>>来阅读std::cin中的文字行。这是悲伤和错误的秘诀。

Answer 2

除了Sam的回答之外，我还建议您在两个if语句之外提取常用功能：

std::string yesNo;

while (yesNo.compare("Y") == 0) {
    cout << "What would you like to do?"
        << endl
        << endl;

    menu();
    getline(cin, bankChoice);

    if (bankChoice == "Cancel")
        return 0;

    if (bankChoice == "Withdraw") {
        withdrawTotal = withdraw(bankAmount);
        bankAmount = withdrawTotal;
    }

    if (bankChoice == "Deposit") {
        depositTotal = deposit(bankAmount);
        bankAmount = depositTotal;
    }

    cout << "You now have $"
        << bankAmount
        << " in your account."
        << endl;

    cout << "Would you like to do anything else?"
        << endl
        << "Y/N: ";

    std::getline(std::cin, yesNo);
}

c ++ While循环打印两次couts

2 个答案: