C++ Do-while loop stopping

Question

I got an assignment where we make a cmd prompt show up and display a flashcard game for multiplication. After inputting a correct answer a prompt shows up and asks the user to go "Again? Y/N." after the second input answer the prompt to ask the user doesn't show up and it's stuck on a "congratulations" message. This happens when I write in code to randomly generate two numbers for the game twice. one outside the while loop, and one inside while loop. If I leave one out the 2nd code for the random numbers it will run fine but will only display the same numbers over again. what I'm asking is how do I fix it so that it won't get stuck after the second answer input?

sample code below:

#include <iostream>

using namespace std;

int main()
{
    int num1, num2, ans, guess, count = 0;
    char choice;

    num1 = rand() % 12 + 1;  
    num2 = rand() % 12 + 1;
    //first number generator.
    ans = num1 * num2;

    do
    {
        {
            cout << num1 << " X " << num2 << " = ";
            cin >> guess;
            cout << "Wow~! Congratulations~! ";
            count++;

            num1 = rand() % 12 + 1;
            num2 = rand() % 12 + 1;
            //second number generator.

        } while (guess != ans);


        cout << "\nAgain? Y/N: ";
        cin >> choice;

    } while ((choice == 'y') || (choice == 'Y'));
    //after two turns the loop stops. Can't make a choice.

    cout << " Thanks for playing! Number of tries:" << count << endl;

    return 0;
}

Answer 1

The problem can be found here:

do
{
    {
        cout << num1 << " X " << num2 << " = ";
        cin >> guess;

As you can see, the second scope has no do statement. As a result it is only a codeblock.

You can solve it by writing a do statement for the second code block.

Because the do is not present in the second bracket ({), the while is interpreted as a while loop:

while (guess != ans);

or

while (guess != ans) {
}

this thus keeps looping until guess is not equal to ans. But since in the loop does not modify any of the two variables, the loop will keep iterating.

---

Other errors: note that the program is still incorrect, since it will claim you have answered the question, regardless of the answer. You can fix it by implementing this as follows:

int main()
{
    int num1, num2, ans, guess, count = 0;
    char choice;

    do {

       num1 = rand() % 12 + 1;
       num2 = rand() % 12 + 1;
       ans = num1 * num2;

       do {
            cout << num1 << " X " << num2 << " = ";
            cin >> guess;
            if(guess == ans) {
                cout << "Wow~! Congratulations~! ";
            } else {
                cout << "No, wrong!\n";
            }
            count++;

        } while (guess != ans);


        cout << "\nAgain? Y/N: ";
        cin >> choice;

    } while ((choice == 'y') || (choice == 'Y'));
    //after two turns the loop stops. Can't make a choice.

    cout << " Thanks for playing! Number of tries:" << count << endl;

    return 0;
}

Answer 2

I'd guess the problem is because your loops aren't quite what you think they are.

do
{

The code above has started a do loop.

    {

I suspect you intended to start another (nested) do loop here--but you left off the do, so it's just a block that gets entered, executed, and exited. Useless and pointless in this case.

        cout << num1 << " X " << num2 << " = ";
        cin >> guess;
        cout << "Wow~! Congratulations~! ";
        count++;

        num1 = rand() % 12 + 1;
        num2 = rand() % 12 + 1;
        //second number generator.

    } while (guess != ans);

You've formatted this as if the while were closing the nested do loop--but since you didn't actually create a nested do loop, this is just a while loop with an empty body. Its meaning would be more apparent with a little re-formatting:

    // second number generator
}

while (guess != ans)
    /* do nothing */
    ;