C ++循环：如何让程序在用户输入无效输入时多次重复“错误”消息

Question

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，如果用户输入“4”进行操作（应该在 1-3 之间），它会正确显示：“您的操作选择无效！请重试，使用 1、2 或 3。 "但是，如果用户为该操作输入了另一个无效数字（例如 5），则不会重复错误消息，而是继续前进。

谁能帮我弄清楚如何让每条错误消息重复，直到为每个提示输入有效数字或字符？

注意：我对编码非常陌生，并且仍在弄清楚 stackoverflow...我想我已经遵循了所有 MCVE 建议/格式。谢谢你！！

#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;
            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);

        switch(operation)
        {
            case 1:
            cout << "You chose addition." << endl;
            num3 = num1 + num2;
            cout << "" << endl;
            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;
                    cout << "What is " <<  num1 << " + " << num2 << " ?: " 
<< endl;
                    cout << "" << endl;
                    cin >> guess;
                    cout << "" << endl;
                    }

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

            case 2:
                cout << "You chose subtraction." << endl;
                num3 = num1 - num2;
                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;
                        cout << "What is " <<  num1 << " - " << num2 << " ?: 
" << endl;
                        cout << "" << endl;
                        cin >> guess;
                        }

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

            case 3:
                cout << "You chose multiplication." << endl;
                num3 = num1 * num2;
                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;
                        cout << "What is " <<  num1 << " * " << num2 << " ?: 
" << endl;
                        cout << "" << endl;
                        cin >> guess;
                        }

                    else 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;
}
/*Sample Run:
Choose an operation.
Enter 1 to add, 2 to subtract, or 3 to multiply:

3

You chose multiplication.
What is 4 * 1 ?:

4

That is correct!

Would you like to play again? Press Y for yes or Q for quit

Y
Thank you for playing! Let's play again!

Choose an operation.
Enter 1 to add, 2 to subtract, or 3 to multiply:

1

You chose addition.

What is 6 + 1 ?:

7

That is correct!

Would you like to play again? Press Y for yes or Q for quit

Y
Thank you for playing! Let's play again!

Choose an operation.
Enter 1 to add, 2 to subtract, or 3 to multiply:

2

You chose subtraction.
What is 5 - 0 ?:

5

That is correct!

Would you like to play again? Press Y for yes or Q for quit

Y
Thank you for playing! Let's play again!

Choose an operation.
Enter 1 to add, 2 to subtract, or 3 to multiply:

1

You chose addition.

What is 7 + 1 ?:

9

That is incorrect. Please try again.

What is 7 + 1 ?:

10

Would you like to play again? Press Y for yes or Q for quit

Y
Thank you for playing! Let's play again!

Choose an operation.
Enter 1 to add, 2 to subtract, or 3 to multiply:

2

You chose subtraction.
What is 7 - 3 ?:

5

That is incorrect. Please try again.

What is 7 - 3 ?:

6
Would you like to play again? Press Y for yes or Q for quit

Q
Thank you for playing! See you next time!


Process returned 0 (0x0)   execution time : 43.057 s
Press any key to continue.
*/

Answer 1

P29：练习算术技巧（if/else，循环）

说明：

“编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。

如果孩子正确回答了方程式，应该会出现一条消息，然后他们可以进入下一个问题（生成两个不同的数字）。

如果孩子回答错误，应该会出现一条消息，并且应该重复该问题（使用相同的数字）。”

终于修好了！：

    #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;
    }

Answer 2

你的 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);

Answer 3

如果您只想让用户重新尝试一次以选择正确的操作，请不要使用 do-while 循环。保持这种方式

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 如果您只想为第一次错误尝试和所有成功的错误尝试打印错误消息，您可以通过以下方式进行：

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);