我不知道为什么这个循环出现故障

I Can't Figure Out Why This Loop Is Malfunctioning

本文关键字：故障 循环 为什么 我不知道      更新时间：2023-10-16

所以我就是想不出我的代码出了什么问题。 当我处理购买时，在我输入酸奶量并被告知去享用它之后，如果人们不输入 P 或 S，我会立即收到我制作的错误消息，然后它立即恢复正常，就像您第一次进入程序时一样，谁能告诉我为什么会这样？ 谢谢！

#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
   string userCommand;
   int creditCount = 0;
   int userInput;
   while (creditCount >= 0)
   {
      cout << "--------Menu--------n" << "P (Process Purchase)n" << "S (Shutdown System)n"
           << "--------Menu--------n" << "Your Choice: ";
      getline(cin, userCommand);
      if (userCommand[0] == 'P' || userCommand[0] == 'p')
      {
         if (creditCount >= 10)
         {
            cout << "You qualify for a free yogurt, would you like to use ten of your credits (Yes or No)?";
            getline(cin, userCommand);
            if (userCommand[0] == 'Y' || userCommand[0] == 'y')
            {
               creditCount = creditCount - 10;
               cout << "You just used 10 credits and now have " << creditCount << " left.n"
                    << "Enjoy your free yogurt!";
            }
            else if (userCommand[0] == 'N' || userCommand[0] == 'n')
            {
               cout << "How many yogurts would you like to buy? ";
               cin >> userInput;
               if (userInput > 0)
               {
                  creditCount = creditCount + userInput;
                  cout << "You just earned " << userInput << " stamps.  You now have " << creditCount
                     << " credits!  Enjoy your yogurt!";
               }
               else
               {
                  cout << "Invalid input, please try processing your purchase again and enter a positive "
                       << "integer.";
               }
            }
            else
            {
               cout << "*Error, please try processing your purchase again and enter either Yes or No*nn";
            }
         }
         else if (creditCount < 10)
         {
            cout << "How many yogurts would you like to buy? ";
            cin >> userInput;
            if (userInput > 0)
            {
               creditCount = creditCount + userInput;
               cout << "You just earned " << userInput << " stamps.  You now have " << creditCount
                    << " credits!  Enjoy your yogurt!nn";
            }
            else
            {
               cout << "Invalid input, please try processing your purchase again and enter a positive "
                    << "integer.";
            }
         }
      }
      else if (userCommand[0] == 'S' || userCommand[0] == 's')
      {
         cout << "*Shutting down system*n";
         return 0;
      }
      else
      {
         cout << "*Error, please enter either P (for Process Purchase) or S (for Shutdown System)*nn";
      }
   }
}

@acid1789正确地指出错误是由于getline之后的空行造成的。从你的代码中我能看出你在这里使用了一个无限循环

while(creditCount >= 0){...}

因为 creditCount 永远不会小于 0，而不是这个你可以使用 

while (true){...}

它只是更好的编程实践。

要纠正您的程序，您只需使用 

cin >> userCommand;

而不是 

getline(cin, userCommand);

希望对您有所帮助。

编辑：- 对不起蟒蛇习惯..

这里的问题是getline返回一个空行。

因此，在您第一次通过循环后，它会回到顶部以阅读另一行。 获取一个空行，这将触发错误情况。

您可以通过在 getline 之后测试空行来解决此问题。

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