Question

Possible Duplicate:
How to validate numeric input C++

How do you do the following:

while (iNumberOfPlayers <2 || iNumberOfPlayers >5)
{
    cout << "Enter number of players (1-4): ";
    cin >> iNumberOfPlayers;
    cin.clear();
    std::string s;
    cin >> s;
}

After looking at the loop I’m thrown in, it looks like cin isn’t getting reset (if I put in x) cin reads X again as long as I’m in the while loop. Guessing this is a buffer issue, any way to clear it?

I then tried:

while (iNumberOfPlayers <2 || iNumberOfPlayers >5)
{
    cout << "Enter number of players (1-4): ";
    cin >> iNumberOfPlayers;
    cin.clear();
    cin.ignore();
}

which works except it reads everything 1 at a time. If I put in “xyz” then the loop goes through 3 times before it stops to ask again.

Answer 1

If the input is not valid, the fail bit is set on the stream. The ! operator used on a stream reads the fail bit (You could also use (cin >> a).fail() or (cin >> a), cin.fail()).

Then you just have to clear the fail bit before trying again.

while (!(cin >> a)) {
    // if (cin.eof()) exit(EXIT_FAILURE);
    cin.clear();
    std::string dummy;
    cin >> dummy; // throw away garbage.
    cout << "entered value is not a number";
}

Please note that if you’re reading from non-interactive input, this would become an infinite loop. So use some variation on the commented error-detection code.