C++ 帮助：循环和开关答案

【问题标题】：C++ help: loops and switchesC++ 帮助：循环和开关
【发布时间】：2017-10-04 19:13:31
【问题描述】：

考虑到它是一个开关，我该如何循环选项 1 和 2？编程新手，很难解决这个问题。任何帮助将不胜感激！

#include <iostream>
using namespace std;

int main()
{
    int userOption;

    cout << "Hello user, what would you like to do?" << endl;
    cout << "Option 1: Display a message" << endl;
    cout << "Option 2: Perform a calculation" << endl;
    cout << "Option 3: Exit program" << endl;
    cin >> userOption;

        switch (userOption)
        {
            char op;
            int num1, num2;

        case 1:
            cout << "Welcome user!" << endl;
            break;
        case 2:
            cout << "Enter + for addition, - for subtraction, * for multiplication or / for division: ";
            cin >> op;
            cout << "Enter two numbers: ";
            cin >> num1 >> num2;
            if (op == '+')
                cout << num1+num2 << endl;
            else if (op == '-')
                cout << num1-num2 << endl;
            else if (op == '*')
                cout << num1*num2 << endl;
            else if (op == '/')
                cout << num1/num2 << endl;
            break;
        case 3:
            cout << "Goodbye!" << endl;
            return 0;
            break;
        default:
            cout << "Please enter valid option!" << endl;

        }
    return 0;
}

【问题讨论】：

您是否尝试过将代码封装在 while 循环中？
您有要循环的案例 1 和 2，以及退出程序的案例 3。如果用循环包围整个菜单，则 1 和 2 将循环，而 3 仍将退出程序。
我应该在哪里插入循环？在哪个语句之前？
StackOverflow 上有大量的计算器作业程序。也许你可以搜索它们，看看菜单是如何处理的。

标签： c++ loops if-statement switch-statement control-flow

【解决方案1】：

简单来说，你可以使用这样的东西：

unsigned int selection = 25;
// Print menu and input selection
while (selection != 3)
{
 // Do stuff
  // Print menu and input selection
}

【讨论】：

【解决方案2】：

使用while 循环覆盖cin 和switch 情况。您可以使用类似下面的内容并使用一个附加变量bContinue，它将决定循环继续多长时间：

int main() 
{
    int userOption;

    cout << "Hello user, what would you like to do?" << endl;
    cout << "Option 1: Display a message" << endl;
    cout << "Option 2: Perform a calculation" << endl;
    cout << "Option 3: Exit program" << endl;
    bool bContinue = true;
    while(bContinue)
    {
        cin >> userOption;

        switch (userOption)
        {
            char op;
            int num1, num2;

        case 1:
            cout << "Welcome user!" << endl;
            break;
        case 2:
            cout << "Enter + for addition, - for subtraction, * for multiplication or / for division: ";
            cin >> op;
            cout << "Enter two numbers: ";
            cin >> num1 >> num2;
            if (op == '+')
                cout << num1+num2 << endl;
            else if (op == '-')
                cout << num1-num2 << endl;
            else if (op == '*')
                cout << num1*num2 << endl;
            else if (op == '/')
                cout << num1/num2 << endl;
            break;
        case 3:
            cout << "Goodbye!" << endl;
            bContinue = false;
            break;
        default:
            cout << "Please enter valid option!" << endl;
        }
    }
    return 0;
}

【讨论】：

【解决方案3】：

使用while 循环创建新变量，但重新格式化一些代码，以便在循环重新开始时继续显示用户选项

cout << "Hello user, what would you like to do?" << endl;

bool bContinue = true;
while(bContinue)
{
    cout << "Option 1: Display a message" << endl;
    cout << "Option 2: Perform a calculation" << endl;
    cout << "Option 3: Exit program" << endl;

    cin >> userOption;

    switch (userOption)
    {
        char op;
        int num1, num2;

    case 1:
        cout << "Welcome user!" << endl;
        break;
    case 2:
        cout << "Enter + for addition, - for subtraction, * for multiplication or / for division: ";
        cin >> op;
        cout << "Enter two numbers: ";
        cin >> num1 >> num2;
        if (op == '+')
            cout << num1+num2 << endl;
        else if (op == '-')
            cout << num1-num2 << endl;
        else if (op == '*')
            cout << num1*num2 << endl;
        else if (op == '/')
            cout << num1/num2 << endl;
        break;
    case 3:
        cout << "Goodbye!" << endl;
        bContinue = false;
        break;
    default:
        cout << "Please enter valid option!" << endl;
    }
}
return 0;

这将使程序在用户看来更好

【讨论】：

【解决方案4】：

使用 do-while 循环，当 userOption 等于 3 时它会停止，因此它会在 userOption 不同于 3 时继续循环，在代码 userOption != 3 中。

示例代码：

#include <iostream>
using namespace std;

int main()
{
    int userOption;

    cout << "Hello user, what would you like to do?" << endl;
    do {
        cout << "Option 1: Display a message" << endl;
        cout << "Option 2: Perform a calculation" << endl;
        cout << "Option 3: Exit program" << endl;
        cin >> userOption;

        switch (userOption)
        {
            char op;
            int num1, num2;

            case 1:
                cout << "Welcome user!" << endl;
                break;
            case 2:
                cout << "Enter + for addition, - for subtraction, * for multiplication or / for division: ";
                cin >> op;
                cout << "Enter two numbers: ";
                cin >> num1 >> num2;
                if (op == '+')
                cout << num1+num2 << endl;
                else if (op == '-')
                    cout << num1-num2 << endl;
                else if (op == '*')
                    cout << num1*num2 << endl;
                else if (op == '/')
                    cout << num1/num2 << endl;
                break;
            case 3:
                cout << "Goodbye!" << endl;
                break;
            default:
                cout << "Please enter valid option!" << endl;

        }
    } while(userOption != 3);
    return 0;
}

输出：

Hello user, what would you like to do?
Option 1: Display a message
Option 2: Perform a calculation
Option 3: Exit program
2
Enter + for addition, - for subtraction, * for multiplication or / for division: 
+
Enter two numbers:
1
1
2
Option 1: Display a message
Option 2: Perform a calculation
Option 3: Exit program
3
Goodbye!

【讨论】：