Question

我正在用C ++编写程序，我希望用户在几个选项之间做出选择，每个选项都不同。在选项的最后，我希望用户能够从菜单中选择不同的选项，但如果用户最初选择选项3，当用户返回菜单时，如果他/她选择1或2终止程序。我该怎么做才能使代码重复？

#include <iostream>
using namespace std;

int main() {
   int play;
   cout << "What do you want to do now?" << endl;
   cout << "Choose a number..." << endl;
   cout << "1) Talk." << endl;
   cout << "2) Vent." << endl;
   cout << "3) Play a guessing game." << endl;
   cout << "4) End." << endl;
   cin >> play;

   while (play == 1){
      //code here
      cout << "What do you want to do now?" << endl;
      cout << "Choose a number..." << endl;
      cout << "1) Talk." << endl;
      cout << "2) Vent." << endl;
      cout << "3) Play a guessing game." << endl;
      cout << "4) End." << endl;
      cin >> play;
   }

   while (play == 2){
      //code goes here
      cout << "What do you want to do now?" << endl;
      cout << "Choose a number..." << endl;
      cout << "1) Talk." << endl;
      cout << "2) Vent." << endl;
      cout << "3) Play a guessing game." << endl;
      cout << "4) End." << endl;
      cin >> play;
   }

   return 0;
}

Answer 1

执行此类操作的常用方法是将整个代码放在while (true)循环中，并在用户选择退出时中断，如下所示：

#include <iostream>
using namespace std;

int main() 
{
    int play;
    while (true)
    {
        cout << "What do you want to do now?" << endl;
        cout << "Choose a number..." << endl;
        cout << "1) Talk." << endl;
        cout << "2) Vent." << endl;
        cout << "3) Play a guessing game." << endl;
        cout << "4) End." << endl;
        cin >> play;

        if (play == 1)
        {
            // code for Talk...
        }
        else if (play == 2)
        {
            // code for Vent...
        }
        else if (play == 3)
        {
            // code for Play a guessing game....
        }
        else if (play == 4)
        {
             // End
            return 0;
        }
        else
        {
            std::cout << "Expected a number between 1 and 4" << std::endl;
        }
    }
}

编辑我还为无法识别的输入添加了测试编辑如果您更喜欢语法，也可以使用switch语句（除非您真的需要，否则请确保没有掉头）（注意：两个代码都是等效的，可能会生成相同的程序集）

int main() 
{
    int play;
    while (true)
    {
        cout << "What do you want to do now?" << endl;
        cout << "Choose a number..." << endl;
        cout << "1) Talk." << endl;
        cout << "2) Vent." << endl;
        cout << "3) Play a guessing game." << endl;
        cout << "4) End." << endl;
        cin >> play;

    switch (play)
    {
    case 1:
        // code for Talk...
        break;
    case 2:
        // code for Vent...
        break;
    case 3:
        // code for Play a guessing game....
        break;
    case 4:
        // End
        return 0;
    default:
        std::cout << "Expected a number between 1 and 4" << std::endl;
    }
}

Answer 2

执行此操作的一种奇特方法是使用switch()，这里是Why the switch statement and not if-else? switch()可以帮助您的程序摆脱非常长的嵌套if-else语句。看看它有多美：

#include <iostream>

int main()
{
    int play = 0;

    while (play != 4)
    {
        std::cout << "What do you want to do now?" << std::endl;
        std::cout << "Choose a number..." << std::endl;
        std::cout << "1) Talk." << std::endl;
        std::cout << "2) Vent." << std::endl;
        std::cout << "3) Play a guessing game." << std::endl;
        std::cout << "4) End." << std::endl;
        std::cin >> play;

        switch (play)
        {
            case 1: // code for talk here
                break;
            case 2: // code for Vent
                break;
            case 3: // code for Play
                break;
            case 4: std::cout << "program will exits!";
        }
    }
    return 0;
}

为什么我的代码中只能使用一个“while”循环？

2 个答案: