无效的int输入陷入无限循环

问题描述

do
{
    cout << "Enter the numerator and denominator of the first fraction: ";
    cin >> a >> b;
    cout << endl;
    cout << "Enter the numerator and denominator of the second fraction: ";
    cin >> c >> d;
    cout << endl;
} while (!validNum(a, b, c, d));

...

bool validNum(int num1, int num2, int num3, int num4)
{
    if (cin.fail() || num2 == 0 || num4 == 0)
    {
        if (num2 == 0 || num4 == 0)
        {
            cout << "Invalid Denominator. Cannot divide by 0" << endl;
            cout << "try again: " << endl;
            return false;
        }
        else
        {
            cout << "Did not enter a proper number" << endl;
            cout << "try again: " << endl;
            return false;
        }
    }
    else
        return true;
}

我想做的是确保分母不为零，他们只输入数字。由零码除法工作正常，但是当您输入一个char值，它进入一个无限循环，不知道为什么。任何想法？

What I am trying to do is make sure the denominator is not zero and that they only enter numbers. The dividing by zero code works fine but when you enter a char value it enters an infinite loop and do not know why. Any ideas?

推荐答案

if (cin.fail() ... )

一旦输入无效的值（例如 char ），流中的failbit将打开， validNum 将始终返回false，导致无限循环。

Once you enter an invalid value (i.e a char), the failbit in the stream will be on and validNum will invariably return false, causing an infinite loop.

您需要清除错误状态，并在每次调用后忽略输入的其余部分：

You need to clear the error state and ignore the rest of the input after each call:

if (std::cin.fail())
{
    std::cin.clear();
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

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