C++循环：如何在用户输入无效输入时多次重复程序

我几乎完成了这项任务，但仍然无法让代码连续显示错误消息，直到输入正确的输入

例如，如果用户为操作输入4，该值应介于1-3之间，则正确显示：您的操作选择无效！请使用1、2或3重试。但是，如果用户为操作输入另一个无效数字，如5，则不会重复错误消息，而是继续向前

有谁能帮我找出如何让每个错误消息重复，直到为每个提示输入有效的数字或字符

注意：我对编码非常陌生，并且仍然了解stackoverflow…我想我已经遵循了所有MCVE建议/格式。谢谢

您的do while循环

do
{
    cout << "Choose an operation." << endl;
    cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
    cout << "" << endl;
    cin >> operation;
    cout << "" << endl;

    if (operation > 3 || operation < 1)
    {
        cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3."
             << endl;
        cout << "" << endl;
        cout << "Choose an operation." << endl;
        cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
        cout << "" << endl;
        cin >> operation;
        cout << "" << endl;
    }
}
while (operation > 3 || operation < 1);

应该是

do
{
    cout << "Choose an operation." << endl;
    cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
    cout << "" << endl;
    cin >> operation;
    cout << "" << endl;

    if (operation > 3 || operation < 1)
    {
        cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3."
             << endl;
    }
}
while (operation > 3 || operation < 1);

---

如果只想给用户一次重新尝试以选择正确的操作，请不要使用Do while循环。把那个街区往这边走

cout << "Choose an operation." << endl;
            cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: "<<endl;
cout << "" << endl;
            cin >> operation;
            cout << "" << endl;

            if (operation > 3 || operation < 1)
            {
                cout << "Your operation choice isn't valid!  Please try 
again, using 1, 2, or 3." << endl;
                cout << "" << endl;
                cout << "Choose an operation." << endl;
                cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " 
<< endl;
                cout << "" << endl;
                cin >> operation;
                cout << "" << endl;
            }

或 如果只想打印第一次错误尝试和所有成功错误尝试的错误消息，可以通过以下方式执行：

int flag=0;
do{
cout << "Choose an operation." << endl;
                cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: "<<endl;
    cout << "" << endl;
                cin >> operation;
                cout << "" << endl;

                if ((operation > 3 || operation < 1)&&flag==0)
                {
                    flag=1;
               cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3." << endl;
                    cout << "" << endl;
                    cout << "Choose an operation." << endl;
                    cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " 
    << endl;
                    cout << "" << endl;
                    cin >> operation;
                    cout << "" << endl;
                }
} while(operation > 3 || operation < 1);

P29：练习算术技能，如果/否则，循环 说明： 写一个程序让孩子练习算术技能

程序应该首先询问需要什么样的练习：+、-、*，并让用户根据需要重复练习多次，直到输入Q

将从0-9生成两个随机数

如果孩子回答正确，就会出现一条信息，然后他们可以转到下一个问题，生成两个不同的数字

如果孩子回答不正确，就会出现一条消息&问题应该重复出现，使用相同的数字

终于修好了！：

---

.我想我已经遵循了MCVE的所有建议/格式。M代表最小值，因此您的开关可以被移除，只需跳过您的内部操作即可。感谢您阅读我想您是这样做的？你已经知道了，但是你忘了跟随。如果你愿意的话，你可以把它作为一个评论发表，尽管如果这个问题已经很好了，理论上它不应该被否定谢谢@Jarod42！这非常有用！

int flag=0;
do{
cout << "Choose an operation." << endl;
                cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: "<<endl;
    cout << "" << endl;
                cin >> operation;
                cout << "" << endl;

                if ((operation > 3 || operation < 1)&&flag==0)
                {
                    flag=1;
               cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3." << endl;
                    cout << "" << endl;
                    cout << "Choose an operation." << endl;
                    cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " 
    << endl;
                    cout << "" << endl;
                    cin >> operation;
                    cout << "" << endl;
                }
} while(operation > 3 || operation < 1);

    #include <iostream>
    #include <cstdio>
    #include <time.h>
    #include <stdlib.h>
    using namespace std;

    int main()
   {
    int operation, num3, guess, num1, num2, temp;
    char play;
    srand(time(0));

    do
    {
      num1 = rand() % 10;
      num2 = rand() % 10;

      if (num1 < num2)
      {
          temp = num1;
          num1 = num2;
          num2 = temp;
      }

        do
        {
            cout << "Choose an operation." << endl;
            cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
            cout << "" << endl;
            cin >> operation;

            if (operation > 3 || operation < 1)
            {
                cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3." << endl;
            }
        }while (operation > 3 || operation < 1);

        switch(operation)
        {
            case 1:
            cout << "You chose addition." << endl;
            num3 = num1 + num2;
            cout << "" << endl;

            do
            {
                cout << "What is " <<  num1 << " + " << num2 << " ?: " << endl;
                cout << "" << endl;
                cin >> guess;
                cout << "" << endl;

                if (guess != num3)
                    {
                    cout << "That is incorrect. Please try again." << endl;
                    cout << "" << endl;
                    }
            } while (guess != num3);

                if (guess == num3)
                    {
                    cout << "That is correct!" << endl;
                    cout << "" << endl;
                    }
            break;

            case 2:
            cout << "You chose subtraction." << endl;
            num3 = num1 - num2;
            cout << "" << endl;

            do
            {
                cout << "What is " <<  num1 << " - " << num2 << " ?: " << endl;
                cout << "" << endl;
                cin >> guess;
                cout << "" << endl;

                if (guess != num3)
                    {
                    cout << "That is incorrect. Please try again." << endl;
                    cout << "" << endl;
                    }
            } while (guess != num3);

                if (guess == num3)
                    {
                    cout << "That is correct!" << endl;
                    cout << "" << endl;
                    }
            break;

            case 3:
            cout << "You chose multiplication." << endl;
            num3 = num1 * num2;
            cout << "" << endl;

            do
            {
                cout << "What is " <<  num1 << " * " << num2 << " ?: " << endl;
                cout << "" << endl;
                cin >> guess;
                cout << "" << endl;

                if (guess != num3)
                    {
                    cout << "That is incorrect. Please try again." << endl;
                    cout << "" << endl;
                    }
            } while (guess != num3);

                if (guess == num3)
                    {
                    cout << "That is correct!" << endl;
                    cout << "" << endl;
                    }
            break;
        }

        do
        {
             cout << "Would you like to play again? Press Y for yes or Q for quit" << endl;
             cout << "" << endl;
             cin >> play;

           if (play != 'Y' && play != 'Q')

            {
                cout << "That is not a valid choice. Please choose Y for yes or Q to quit. " << endl;
                cout << "" << endl;
            }

        }

        while(play !='Y' && play !='Q');

        if (play == 'Y')
        {
        cout << "Thank you for playing! Let's play again!" << endl;
        cout << "" << endl;
        }

        else
        {
        cout << "Thank you for playing! See you next time!" << endl;
        cout << "" << endl;
        }

     }
     while(play=='Y');

    return 0;
    }