checking for user integer input with cin gives infinite loop

Question

I'm trying to print an error message if the user does not enter anything into the input prompt, and if what they enter is zero or less.

void checkScoreInputed(int* qaltScores, int i){
    while(true){
        // cin.clear(); here?
        if ((cin >> qaltScores[i]) && (qaltScores > 0)){
            // also tried placing cin.clear() here. 
            break;} else // else is optional
        cout << "Please supply a positive number for the score: ";
    }
}

I've tried placing cin.ignore() and cin.clear() both before and after the if statement, but I am still getting an infinite loop of cout << "Please supply...." after the user enters a non-integer value, like a character. How can I fix this?

Thing is, I'm not sure where I should place the clear(), if necessary. — LazerSharks, Mar 02 '13 at 22:47
You need to call them after the input goes into a bad state. In your code, that is most logically right with the output. — chris, Mar 02 '13 at 22:49
@chris Thanks Chris, your comment, which should be an answer, helped and made it work! — LazerSharks, Mar 02 '13 at 22:50
The answer provided that around the same time as me :) I was going for the very brief explanation of why you put it there. — chris, Mar 02 '13 at 22:56

score 2 · Accepted Answer · edited May 23 '17 at 12:03

2

You forgot the [i] in

if ((cin >> qaltScores[i]) && (qaltScores[i] > 0))
                                         ^^^

Without it, you're checking the value of the pointer, not the number you've just read.

You also need to call cin.clear() and cin.ignore().

void checkScoreInputed(int* qaltScores, int i) {
    while(true) {
        if ((cin >> qaltScores[i]) && (qaltScores[i] > 0)){
            break;
        }
        cout << "Please supply a positive number for the score: ";
        cin.clear();
        cin.ignore(10000,'\n');
    }
}

See Why would we call cin.clear() and cin.ignore() after reading input?

edited May 23 '17 at 12:03

Community

1
1

answered Mar 02 '13 at 22:45

NPE

486,780
108
951
1,012

Oh, woops. Thanks. But that did not fix my problem. I also had the infinite loop problem before I added that last condition of qaltScores[i] > 0. – LazerSharks Mar 02 '13 at 22:46
should I place them outside or inside the if statement? – LazerSharks Mar 02 '13 at 22:49
also adding that cin.ignore(1000, '\n') part turned out to be really important. – LazerSharks Mar 02 '13 at 22:58

checking for user integer input with cin gives infinite loop

1 Answers1