iostream - How to use cin.fail() in c++ properly

Question

I'm writing a program where I get an integer input from the user with cin>>iUserSel;. If the user puts in a letter, the program goes to an infinite loop. I tried to prevent that with the code below, but the program goes to an infinite loop and prints out "Wrong! Enter a #!". How can I fix my program?

cin>>iUserSel;
while (iValid == 1)
{
        if (cin.fail())
        {
                cin.ignore();
                cout<<"Wrong! Enter a #!"<<endl;
                cin>>iUserSel;
        }//closes if
        else
                iValid = 0;
}//closes while

I found some information on this at Correct way to use cin.fail() and C++ cin.fail() question , but I didn't understand how to use them to fix my issue.

question from:https://stackoverflow.com/questions/66065948/is-cin-fail-with-my-while-loop-causing-my-output-to-infinitely-loop

Answer 1

When cin fails, you need to clear the error flag. Otherwise subsequent input operations will be a non op.

To clear the error flags, you need to call cin.clear().

Your code would then become:

cin >> iUserSel;
while (iValid == 1)
{
    if (cin.fail())
    {
        cin.clear(); // clears error flags
        cin.ignore();
        cout << "Wrong! Enter a #!" << endl;
        cin >> iUserSel;
    }//closes if
    else
        iValid = 0;
}//closes while

I would also suggest you change

cin.ignore(); 

to

cin.ignore(numeric_limits<streamsize>::max(), '
'); 

In case the user enters more than one letter.