當輸入錯誤輸入時無限循環無限循環

Question

爲什麼當輸入錯誤輸入時無限循環？我該如何糾正？

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

如果你有一個cin無法解析的輸入，流將處於錯誤狀態。

這裏是你如何清除錯誤狀態，則忽略該項輸入一個例子：

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，它試圖忽略不正確的之前清除輸入流的錯誤狀態是非常重要的字符。希望有幫助 -

Answer 2

在輸入流遇到錯誤後，流將處於失敗狀態。您明確地必須清除該流上的故障位並在之後將其清空。嘗試：

#include <limits> 
#include <iostream> 

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

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

您可以檢查輸入通過檢查好（）不好（），失敗（）或EOF的返回值升高（）的錯誤。這些函數只是返回內部狀態位的狀態（如果設置了相應位，則返回true - 除了good（），顯然，如果所有內容都按順序返回）。