c++ isalnum endless loop

Question

Greetings!

Lets cut the excessive intro this time and get straight to the point.

I have a problem in C++ using the isalnum method.

the code:

int playAgainst = 0;
do
{
    cout << "Who do you want to play against?(1/2)\n";
    cout << "1: Human player\n";
    cout << "2: Computer player\n";
    cin >> playAgainst
} while(!isalnum(playAgainst) && playAgainst != 0);

As seen in the code, I'm providing the user with a choice. Play against human or play against a computer.

What I want is, as long as the user enters anything else then an integer value(cin >> playAgainst) to repeat the question. However, If i enter a char, or string value, it keeps looping endlessly. I am not 100% sure, but it would be obvious, if the problem is, that the non int value is already saved as the value for playAgainst.. How can I check in this bit of code if the input value is int before saving it?

Or is the only possibility to save as a char/string and then check?

If the latter is the case, a new problem arises. isalnum only accepts int as parameter, atleast from what I know. How will I check if that string or char is an int?

Thank you for taking the time to read. And hopefully Ill be accepting a reply as answer soon ^^

Thanks everyone for the answers. I have gotten what I wanted, and everything has been solved.

The reason I chose for the accepted answer, is well... because initially, it made my code work the way I want it to. I want to accept multiple answers though..

Answer 1

Make playAgainst a char and compare against '0', not 0. Right now, the user has to enter the ASCII (or whatever your character set is) code for the character '1' or '2'.

isalnum won't work on ints outside the valid range of char, except for EOF. (The fact that it takes an int argument is a leftover from C, which has different integer promotions rules than C++. to accomodate for EOF.)