While loop acting weird in regards to input

Question

Been working on a simple school project but I've run into a small problem in regards to validation of user input via the use of a while loop. The following code is used to do so:

cout << "How much woud you like to bet?[100, 300, 500]" << endl;
    cin >> int_input;
    if (cin.fail()){
        int_input = 0;
    }

     //Validate check
     while(int_input!=100 && int_input!=300 && int_input!=500){
        cout << "Please enter a valid bet [100, 300, 500]" << endl;
        cin >> int_input;
        if (cin.fail()){
            int_input = 0;
        }
     }

The issue arises when a non-integer is entered and the loop ends up spitting out the cout msg over and over again, skipping the request for new input. I assume that a non-integer always returns true for the while loop, but the program should still ask for user input, right?

The cin.fail is a recent addition and might not be necessary as it doesn't solve the problem, although I leave the code as it as it is.

You need to reset cin. You told it to read an int, gave it bad data, which puts the stream in a bad state where it doesn't block. — Carcigenicate, Jul 07 '17 at 15:59
Fwiw, even if you clear, you still need to skip the bad data or you'll be right back where you were. — WhozCraig, Jul 07 '17 at 16:00
Short answer: `cin >>` is bad and you shouldn't use it, especially not for user input. `std::getline` is much better behaved. — melpomene, Jul 07 '17 at 16:00
Possible duplicate of [cin.clear() doesn't reset cin object](https://stackoverflow.com/questions/7413247/cin-clear-doesnt-reset-cin-object) — Carcigenicate, Jul 07 '17 at 16:01
Not a perfect dupe, but the target should explain everything. — Carcigenicate, Jul 07 '17 at 16:01

score 3 · Accepted Answer · answered Jul 07 '17 at 16:02

If you have an error on the stream, you set your value to 0. So the loop is run again... and the error's still on the stream. Repeat.

You need to clear the error flag.

cin.clear();

Then extract enough "bad" data to get to the good part, or you'll just be right back where you started.

While loop acting weird in regards to input

1 Answers1