Question

I am trying to parse input from a file to represent a standard deck of cards (i.e. 2C represents the two of clubs). However, my solution is not working as expected, and is declaring all inputs to be invalid. I can’t see any logical errors in my code, so I wanted to get a second opinion. The code is below:

/*
 * Determines if the input string is valid.
 * 
 * A string is considered valid if it begins with either a number (2-10) 
 * or a letter (J/j, Q/q, K/k) to deetermine rank, followed by a letter to
 * determine suit (C/c, D/d, H/h, S/s).
 */
bool inputValidator(string cardData)
{
    if (cardData.length() == 2) //Input string is two characters long
    {
        if (cardData[0] < '2' || cardData[0] > '9'
            || cardData[0] != 'J' || cardData[0] != 'j'
            || cardData[0] != 'Q' || cardData[0] != 'q'
            || cardData[0] != 'K' || cardData[0] != 'k'
            || cardData[0] != 'A' || cardData[0] != 'a')
        {
            cout << "Card with data " << cardData << " has an invalid rank." << endl;
            return false;
        }
        if (cardData[1] != 'C' || cardData[1] != 'c' //Parse suit
            || cardData[1] != 'D' || cardData[1] != 'd'
            || cardData[1] != 'H' || cardData[1] != 'h'
            || cardData[1] != 'S' || cardData[1] != 's')
        {
            cout << "Card with data " << cardData << " has an invalid suit." << endl;
            return false;
        }
        return true;
    }
    else if (cardData.length() == 3) //Input string is three characters long
        //This occurs only if the number is 10.
    {
        if (cardData[0] != '1' || cardData[1] != '0') //Parse rank
        {
            cout << "Card with data " << cardData << " has an invalid rank." << endl;
            return false;
        }
        if (cardData[2] != 'C' || cardData[2] != 'c' //Parse suit
            || cardData[2] != 'D' || cardData[2] != 'd'
            || cardData[2] != 'H' || cardData[2] != 'h'
            || cardData[2] != 'S' || cardData[2] != 's')
        {
            cout << "Card with data " << cardData << " has an invalid suit." << endl;
            return false;
        }
        return true;
    }
    return false;
}

If there are any logical flaws (or an inherently better way to do this), I would appreciate being told. Thanks.

Answer 1

You’re writing clauses like this:

cardData[2] != 'D' || cardData[2] != 'd'

Which will always be true, as the variable being tested can’t be both values at the same time. You probably meant to use && rather than ||.

You could certainly simplify the logic, for example by converting the input to lower or upper case before comparing it.