我的cin在while循环中被忽略 [英] My cin is being ignored inside a while loop

问题描述

我试图在我的第一个C ++程序中编写一个简单的问题和数字检查器。
问题是，当我输入一个类似一两个或三个的字符串时，程序会变成无限循环，它会忽略cin函数，将生命重新分配给一个数字。

I am trying to code a simple question and number checker into my first C++ program. Problem is, when I type a string like one two, or three, the program becomes and infinite loop and it ignores the cin function to re-assign lives to a number.

cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << endl;
cin >> lives;


while(lives != 1 && lives != 2 && lives != 3 && !isdigit(lives))
{
    cout << "You need to input a number, not words." << endl;
    cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << endl;
    cin >> lives;
}

以下是我当前的代码及您的建议：

Here is my current code with your suggestions:

    cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << endl;
std::cin.ignore();
std::cin.clear();
if (std::cin >> lives)
{


    while(lives != 1 && lives != 2 && lives != 3)
    {
        cout << "You need to input a number, not words." << endl;
        cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << endl;
        cin >> lives;
    }

}

推荐答案

#include <iostream>
#include <limits>

int main()
{
    int lives = 0;
    std::cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << std::endl;


    while(!(std::cin >> lives) || lives < 1 || lives > 3)
    {
        std::cout << "You need to input a number, not words." << std::endl;
        std::cout << "How many lives would you like 1 (hard), 2 (medium), or 3 (easy)?" << std::endl;
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }

    return 0;
}

好吧。 std :: cin.clear（）; 负责重置失败位。 std :: cin.ignore 删除流中留下的任何错误输入。我已经调整停止条件。 （ isDigit 是一个冗余检查，如果生活在1和3之间，那么显然它是一个数字）。

Alright. std::cin.clear(); takes care of resetting the fail bits. std::cin.ignore removes any wrong input left in the stream. And I've adjusted the stop condition. (isDigit was a redundant check, if lives is between 1 and 3 then clearly it's a digit).

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