c++ - 如何修复 switch 语句处于 while 循环时不断发生的无限循环

Question

我是 c++ 的新手，对于一项作业，我有一个程序需要在一段时间内进行切换，但我一直陷入无限循环

我已经尝试寻找解决它的方法，但由于我不擅长 c++，所以我很难得到我的错误

#include <iostream>
#include <stdio.h>

using namespace std;

int main(void)
{
   float length, width, perimeter, area;
   char ans;

   cout<<"Please enter the length of the rectangle: \n";
   cin>>length;
   cout<<"Please enter the width of the rectangle: \n";
   cin>>width;
   cout<<"What do you wish to do with these values?\n";
   cout<<"Choose an option from the menu: \n";
   cout<<"1 - Calculate Perimeter\n";
   cout<<"2 - Calculate Area\n";
   cout<<"3 - Quit\n";
   cout<<"Please enter your choice: \n";
   cin>>ans;


   while (ans != '3')
   {
      printf("give option: "); //found this online
      ans = getchar();         //this too

      switch (ans)
      {
         case '1' :
            perimeter=2*(length+width);
            cout<<"The perimeter of the rectangle with length "<<length<<" and width "<<width<<" is "<<perimeter<<endl;
            break;

         case '2' :
            area=length*width;
            cout<<"The area of the rectangle with length "<<length<<" and width "<<width<<" is "<<area<<endl;
            break;

         default :
            cout<<"Invalid Entry, please only select options from menu"<<endl;

      }
   }

   printf("Program finished...\n"); //this was online too
   return 0;
}

当我输入选项 2 或 1 时，有一个无限循环，我似乎无法解决这个问题。我不习惯在这个网站上格式化，请原谅我格式化代码的方式

Answer 1

getchar() 不是在那里使用的正确函数。它返回所有字符、空格、换行符等。

如果紧接着添加一行输出 ans 的值，您会注意到分配给 ans 的所有值。

ans = getchar();
cout << "ans: " << (int)ans << endl;

要从流中跳过空格，请使用

cin >> ans;

此外，在while 循环中获取ans 的逻辑是有缺陷的。它应该在 switch 语句之后。否则，您的程序会在第一次执行 switch 语句之前尝试读取 ans 两次。

这是适用于我的相关代码的更新版本。

cout << "Please enter your choice: \n";
cin >> ans;

while (ans != '3')
{
   switch (ans)
   {
      case '1' :
         perimeter=2*(length+width);
         cout<<"The perimeter of the rectangle with length "<<length<<" and width "<<width<<" is "<<perimeter<<endl;
         break;

      case '2' :
         area=length*width;
         cout<<"The area of the rectangle with length "<<length<<" and width "<<width<<" is "<<area<<endl;
         break;

      default :
         cout<<"Invalid Entry, please only select options from menu"<<endl;
   }

   cout << "Please enter your choice: \n";
   cin >> ans;
}