Using an enum as an array index

Is this good programming style?

I think so. I do the same thing quite frequently.

Is there a better way to do it?

class Button
{
public:
    // Used for array indexes!  Don't change the numbers!
  enum State {
    NORMAL = 0,
    PRESSED,
    CLICKED,
    NUMBER_OF_BUTTON_STATES
  };
};

Drawback is that NUMBER_OF_BUTTON_STATES is now a valid Button::State value. Not a big issue if you are passing these values around as ints. But trouble if you are actually expecting a Button::State.

Using an enum as an array index doesn’t feel right.

It’s fine. Just DOCUMENT it, so the next guy knows what’s going on! (That’s what comments are for.)

Do I have to specify the values of the enum?

With no ‘=’ assignment, enum’s are supposed to start at zero and increment upwards.

If a enum entry has an ‘=’ assigned value, subsequent non ‘=’ enum entries continue counting from there.

Source: The Annotated C++ Reference Manual, pg 113

That said, I like to specify the initial value just to make the code that much clearer.