Suppose you write a simple program to play a number guessing game: “I’m thinking of a whole number between X and Y…” where the user attempts to guess the number in order to win. Failures that require feedback to the user come in three main flavors:

1. The user guessed incorrectly
2. The user’s guess was out of range
3. The user did something silly, like enter a non-integer value

The do..while form

You can do this with a loop, of course. A do..while loop seems like a natural choice here. What I don’t like is the validation and user feedback in the while clause. You’d call out to a method that hides all of the validation logic, and returns true or false. This is OK, but that boolean method will have a side effect, i.e. feedback to the user.

do {
    //increment guess count
    //ask for input
    //read in input
} while (
    //input is wrong
);

The recursive form

An alternative implementation might use recursion:

static void elicitGuess() {
    //increment guess count
    //ask for input
    //read in the input
    //validate input inline
        //Failure:
            //display relevant feedback
            //elicitGuess()
        //else return
}

I find this second way to be more natural and readable. But it also feels like the wrong thing to do, though I can’t articulate why. Maybe it’s because any time I’ve seen code that followed this kind of pattern, I’ve seen it written using loops.

Thoughts?