在while循环C ++中切换语句答案

【问题标题】：Switch statements inside while loop C++在while循环C ++中切换语句
【发布时间】：2014-12-28 11:13:51
【问题描述】：

试图编写一个程序来计算一个盒子的体积、表面积或“周长”。我希望能够为每个主题输入一个字母，并在计算出该主题之后，然后为下一个主题输入一个字母。该程序还希望在键入 Q 时结束。我相信我的数学是正确的，但这个程序对我不起作用。它编译得很好，但体积根本不会计算，尽管其他两个主题会。我也得到了三行答案，当我输入第二个字母作为第二个值时，程序运行疯了。非常感谢任何和所有帮助。感谢您的宝贵时间。

include <iostream>
include <iomanip>

using namespace std;

const char SENTINEL = 'Q';//found this suggestion online to quit a program

int main ()
{

char V, A, G, inputChar;
float length, width, depth, totalV, totalA, totalG;

cout<<"Enter character V for Volume, character A for Surface Area,\n";
cout<<"character G or Girth plus Depth or Q to quit\n"<<endl;
cin>>inputChar;// pick letter
while (inputChar!=SENTINEL)// if not Q then check the if-ele statments
{
      switch (inputChar)
      case 'V':
      {
                cout<<"Enter Length, Width, and Depth for Volume\n";
                cin>>length, width, depth;
                totalV=length*width*depth;//math for volume
                cout<<"The Volume = "<<totalV<<endl;
                break;
      }
      case 'A':
      {
               cout<<"Enter Length, Width, and Depth for Surface Area\n";
               cin>>length, width, depth;
               totalA=2*length*width+2*width*depth+2*length*depth;//math for area
               cout<<"The Surface Area = "<<totalA<<endl;
               break;
      }
      case 'G':
      {
               cout<<"Enter Length, Width, and Depth for Girth\n";
               cin>>length, width, depth;
               totalG=2*(length+width)+depth;//math for girth
               cout<<"The Girth = "<<totalG<<endl;
               break;
      }          
}
      system ("pause");
      return 0;
}

【问题讨论】：

标签： c++ while-loop switch-statement

【解决方案1】：

除了 Elliot 的回答之外，我发现您的程序有一些改进，如果没有这些改进，我认为它不会编译。就像包含语句中的“#”和错误的开关块。即使输入多个值，我们也需要级联 >> 而不是逗号。

这是一个可以编译的代码：

#include <iostream>
#include <iomanip>

using namespace std;

const char SENTINEL = 'Q';//found this suggestion online to quit a program

int main ()
{

char V, A, G, inputChar;
float length, width, depth, totalV, totalA, totalG;

cout<<"Enter character V for Volume, character A for Surface Area,\n";
cout<<"character G or Girth plus Depth or Q to quit\n"<<endl;
cin>>inputChar;// pick letter

while (inputChar!=SENTINEL)// if not Q then check the if-ele statments
{
      switch (inputChar)
      {
         case 'V':

                cout<<"Enter Length, Width, and Depth for Volume\n";
                cin>>length>>width>>depth;
                totalV=length*width*depth;//math for volume
                cout<<"The Volume = "<<totalV<<endl;
                break;

         case 'A':

               cout<<"Enter Length, Width, and Depth for Surface Area\n";
               cin>>length>>width>>depth;
               totalA=2*length*width+2*width*depth+2*length*depth;//math for area
               cout<<"The Surface Area = "<<totalA<<endl;
               break;

         case 'G':

               cout<<"Enter Length, Width, and Depth for Girth\n";
               cin>>length>>width>>depth;
               totalG=2*(length+width)+depth;//math for girth
               cout<<"The Girth = "<<totalG<<endl;
               break;
      }

   cout<<"Enter character V for Volume, character A for Surface Area,\n";
   cout<<"character G or Girth plus Depth or Q to quit\n"<<endl;
   cin>>inputChar;// pick letter          
}
      return 0;
}

【讨论】：

【解决方案2】：

写

while ( cin >> inputChar && inputChar != SENTINEL )
{
//...

而不是

cin>>inputChar;// pick letter
while (inputChar!=SENTINEL)//

你也可以写

auto prompt = []
{
    cout << "\nEnter character V for Volume, character A for Surface Area,\n";
    cout << "character G or Girth plus Depth or Q to quit\n"<<endl;
};

while ( prompt(), cin >> inputChar && inputChar != SENTINEL )
{
//...

或者

auto prompt = []
{
    cout << "\nEnter character V for Volume, character A for Surface Area,\n";
    cout << "character G or Girth plus Depth or Q to quit\n"<<endl;
};

prompt();
while ( cin >> inputChar && inputChar != SENTINEL )
{
    switch (inputChar)
    {
    case 'V':
    {
    //...
    }

    //...
    }

    prompt();
}

【讨论】：

【解决方案3】：

您永远不会更新您的inputChar。在您的while 循环结束时读取另一个char，

  cin>>inputChar;
}
system ("pause");

否则，当 char 与您的 switch case 或 sentinel 不匹配时，它将进入紧密循环（可能 CPU 使用率较高）。

【讨论】：

【解决方案4】：

您需要在 while 循环内再次提示用户输入数据：

do
{
    cout << "Enter character 'V' for Volume, character 'A' for Surface Area,\n";
    cout << "character 'G' for Girth plus Depth or 'Q' to quit\n"<<endl;
    //Right here before the switch statement
    cin >> inputChar;
    switch (inputChar)
    {
        //I also recommend stacking your cases, for lower case and upper case support:
        case 'V':
        case 'v':
        {
            //
        }
        case 'A':
        case 'a':
        {
            //
        }
        case 'G':
        case 'g':
        {
            //
        }
        //Add a default case if they're not any of the above letters
        default:
        {
            cout << inputChar << " is not valid input!";
        }
    }
} while (inputChar != SENTINEL);

【讨论】：

【解决方案5】：

只需添加 cin>>inputChar; 在 while 循环结束时。而已。之后编译并运行。您将获得预期的输出。 :-)

-贾耶什

【讨论】：