Enumeration?

[vince510]

I am on the topic of user-defined types and I can't understand enumeration. The example in the book is confusing and doesnt make any sense to me. Could someone explain it any better?

The example I got was

enum Animal (CAT, DOG, RODENT);

I understand that Animal is the type and CAT, DOG, and RODENT are the literal constants. I just cant think of anywhere someone would use this.

[Duthomhas]

Everything in the computer is represented by a number.

Often, though, we want to think in terms of real things -- and we don't care what the actual number is.

So, for example, an enumeration for the faces on the cards in a deck can be simply:

enum CardFace
  {
  Spades,
  Diamonds,
  Clubs,
  Hearts
  };

The actual value of the number is not important. The programmer can use it with impunity:

struct Card
  {
  CardFace face;
  unsigned suit;
  };

Card my_card;
my_card.face = Spades;
my_card.suit = 1;

Now, if you want to know if a card is the Ace of Spades, just check it:

if ((my_card.face == Spades)
&&  (my_card.suit == 1))
  {
  cout << "Yes, I am the Ace of Spades!\n";
  }

It has no other purpose but that very abstraction from pure numbers to the kinds of things we think about, in the language we think about it.

Hope this helps.