c++ - 菜单中的 C++ 循环

Question

在我的代码中存在一个问题，即使我输入“Q”或“q”，程序也会不断循环菜单。这里有什么问题？这是代码：

{
    char selection;
    do {
        cout << "Add a county election file         A" << endl;
        cout << "Show election totals on screen     P" << endl;
        cout << "Search for county results          S" << endl;
        cout << "Exit the program                   Q" << endl;
        cout << "Please enter your choice: ";
        cin >> selection;
    } while ((selection != 'Q' || selection != 'q'));
    return 0;
}

Answer 1

您想&&在测试中使用 And ( ) 运算符，而不是 Or ( ||) 运算符。否则，selection != 'Q'and之一selection != 'q'将始终为真，并且您的循环将永远不会退出。

Answer 2

正如所指出的，||不满足您的要求。您需要使用&&运算符。

如果你按q，那么情况就是这样。

(selection != 'Q' || selection != 'q')
|---------------|    |--------------|
    true                  false

如果你按Q，那么情况就是这样。

(selection != 'Q' || selection != 'q')
|---------------|    |--------------|
    false                  true

循环应该是这样的。

while((selection != 'Q' && selection != 'q'));

Answer 3

试试这个：

} while((selection != 'Q' && selection != 'q'));

Answer 4

使用toupper().

如果你这样做， while ( toupper(selection) != 'Q' )你将不需要检查大小写。

#include <iostream>
#include <stdio.h>
using namespace std;

int main(void)
{



    char selection;
    do {
        cout << "The Menu" << endl;
        cout << "____________________________________" << endl;
        cout << "Add a county election file         A" << endl;
        cout << "Show election totals on screen     P" << endl;
        cout << "Search for county results          S" << endl;
        cout << "Exit the program                   Q" << endl;
        cout << "____________________________________" << endl;
        cout << "Please enter your choice: ";
        cin >> selection;
    } while ( toupper(selection) != 'Q'  );



  cout<<" \nPress any key to continue\n";
  cin.ignore();
  cin.get();

   return 0;
}