当输入错误输入时无限循环无限循环

Question

为什么当输入错误输入时无限循环？我该如何纠正？

int operation; 
    while (true) { 
     cout << "What operation would you like to perform? Enter the number corresponding to the operation you would like to perform. "; 
     cin >> operation; 
     if (operation >= 1 && operation <= 5) break; 
     cout << "Please enter a number from 1 to 5, inclusive.\n"; 
    } 

Answer 1

如果你有一个cin无法解析的输入，流将处于错误状态。

这里是你如何清除错误状态，则忽略该项输入一个例子：

int operation; 
while (true) { 
cout << "What operation would you like to perform? Enter the number corresponding to the operation you would like to perform. "; 
     cin >> operation; 
     if (cin.fail()) 
     { 
      cout << "Not a number " << endl; 
      cout << "Please enter a number from 1 to 5, inclusive.\n"; 
      cin.clear(); 
      cin.ignore(100, '\n'); 
      cin >> operation; 
     } 
     if (operation >= 1 && operation <= 5) break; 
     cout << "Please enter a number from 1 to 5, inclusive.\n"; 
    } 

注意，它试图忽略不正确的之前清除输入流的错误状态是非常重要的字符。希望有帮助 -

Answer 2

在输入流遇到错误后，流将处于失败状态。您明确地必须清除该流上的故障位并在之后将其清空。尝试：

#include <limits> 
#include <iostream> 

... 
... 
// erroneous input occurs here 

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

您可以检查输入通过检查好（）不好（），失败（）或EOF的返回值升高（）的错误。这些函数只是返回内部状态位的状态（如果设置了相应位，则返回true - 除了good（），显然，如果所有内容都按顺序返回）。