在循环C ++中切换语句

Question

试图编写一个程序来计算盒子的体积，表面积或“周长”。 我希望能够为每个主题输入一个字母，然后在计算该主题后，输入下一个主题的字母。 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，但音量根本不会计算，尽管其他两个主题会。 我还得到了三行答案，当我输入第二个字母作为第二个值时，程序就疯了。 任何和所有的帮助非常感谢。 谢谢你的时间。

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;
}

Answer 1

除了Elliot的答案之外，我发现你的程序有一些改进，没有它我认为它不会编译。 像include语句中的'＃'和错误的开关块一样。 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;
}

Answer 2

写

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

代替

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 )
{
//... 

要么

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();
}

Answer 3

你永远不会更新你的inputChar 。 在while循环结束while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，它将进入一个紧密循环（可能具有高CPU使用率）。

Answer 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);

Answer 5

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

-Jayesh