Validating One of Two Choices

Question

This is working for "draw" but not for discard". I just want it to validate whether the input is one of the two. I run into this problem frequently and don't understand why. Does anyone see the problem?

while(!(choice.equalsIgnoreCase("draw") && !(choice.equalsIgnoreCase("discard"))))

Thanks.

Answer 1

Simplify it (and watch your parentheses in the future):

while(choice.equalsIgnoreCase("draw") || choice.equalsIgnoreCase("discard")) {
    // code
}

What your code is currently doing is this:

!(choice.equalsIgnoreCase("draw") && !(choice.equalsIgnoreCase("discard")))

Pay close attention to that negation. It's closing the entire expression, because you've opened up the paren too wide. That would evaluate to true only if you entered in "discard".

If you meant to say this:

!choice.equalsIgnoreCase("draw") && !choice.equalsIgnoreCase("discard"))

Then that contradicts what you're trying to evaluate - you want to check to see if one of those evaluates to true. If you correct the parentheses, then it would still be incorrect, as it only evaluates if both of those statements are false.

Answer 2

You forgot to close a parenthesis for the "draw" test, you could use

while (!(choice.equalsIgnoreCase("draw")) && 
       !(choice.equalsIgnoreCase("discard")))

or

while (!choice.equalsIgnoreCase("draw") && 
       !choice.equalsIgnoreCase("discard"))

or use De Morgan's Laws like

while (!(choice.equalsIgnoreCase("draw") || 
         choice.equalsIgnoreCase("discard")))

Answer 3

If you're trying to check if the input is one of the two, you want to do

while(choice.equalsIgnoreCase("draw") || choice.equalsIgnoreCase("discard"))

Right now you're only entering the loop when choice is neither "draw" nor "discard"