cin.get() getting too much

Question

I want a user to enter a char. I want to filter what they enter and take only the first char they type.

int main(){
    while (true){
        char n = readOption();
        cout << n << std::endl;
    }
    return 0;
}


char readOption() {
    char input = '\0';
    while (input != '\n') {
        input = cin.get();
        if (isalpha(input)) {
            break;
        }
    }
    return toupper(input);
}

If I enter 13@ jkjoi, the console prints.

J
K
J
O
I

I only want it to print J. Why is it printing the other letters as well?

Answer 1

It is printing all of the characters because (after you fix your semi-colon error) you loop forever:

while (true)
{
    char n = readOption();
    cout << n << std::endl;
}

This will call your read function over and over, forever! Your read function loops until he gets an alpha character, so it ignores "13@ " and then grabs 1 character for each iteration of the while (true) loop. If you want it to stop after reading the first alpha character, don't loop:

char n = readOption();
cout << n << std::endl;

Updated

With your comment, you can actually re-write your code entirely:

std::locale loc;
char c = '\0';
do
{
    // get a character with error checking
    while (!(std::cin >> c))
    {
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }
} while (!std::isalpha(c, loc));
// ignore the rest of the input
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

Answer 2

Because you asked it to.

You perform this in a loop, forever.

If you only want to do it once, then simply do it once. Remove your loops.