C/C++ question on enumerators?

Can I apply Mathematical operations on the enum?

i.e. some nonsensical code

enum animal {
  CAT       = 1,
  DOG       = 2,
  Elephant  = 3,
  Monkey   = 4
}
...

animal things = ;

for (things = CAT; things <= Monkey; things++)
{
  ...

}

Mainly what I question is; can I do the “things++” ?

if so, what would happen if I let it overflow ? that is to say, if I did not have the condition of “things <= Monkey”
and just let “things++” run off? would it automatically jump back down to CAT or would it become undefined with a int value of 5+ ?

Thanks!

Chris

This appeases the compiler…

for (things = CAT; things <= Monkey; things = (animal)(things + 1) )

Otherwise you have to override the ++ operator for the animal data-type.

would it automatically jump back down to CAT

No.

or would it become undefined with a int value of 5+ ?

Yes,

Whoa!

Can you explain this bit

things = (animal)(things + 1)

? Specifically what comes after the "=" How and why does this work ( I tested it and you are correct ) but it seems out of typical language.

Thanks!

Chris

I guess the things++ operation (increment the value of 'things') doesn't work so you have to spell it out:

Take the value of 'things': things Add the value 1: (things + 1) Treat that value as if it were an 'animal' instead of an integer. This is called "casting": (animal)(things + 1) Store the new 'animal' in the location named 'things': things = (animal)(things + 1);

CB, john

Thanks!

So, allow me to understand a bit more...

(things + 1) would equate to an integer (kinda like an auto cast to an int as a simpler form) , but the resulting integer really isn't an animal unless manually telling it what cast you want?

i.e. ?

things = (animal) 4; // would result into a monkey ?

Seems as though C would be more flexible if you could work on values of an enum directly. But oh well.

Thank you again!

Chris Chris

neurascenic: So, allow me to understand a bit more...

(things + 1) would equate to an integer (kinda like an auto cast to an int as a simpler form)

Yes, the result is an "int".

but the resulting integer really isn't an animal unless manually telling it what cast you want?

Yes.

i.e. ? things = (animal) 4; // would result into a monkey ?

Almost correct. The result is a "Monkey". Remember, C(++) is case-sensitive.

Seems as though C would be more flexible if you could work on values of an enum directly.

I think C is less restrictive and allows the use of increment. C++ has much stricter rules regarding assignment.

But oh well.

I do like C++ but things like this make me miss ObjectPascal.

If C++ allowed automatic casting of enum types there would be no safety advantage to using the enum over using an int and a bunch of defines (the original C way). When you create an enumeration you are saying you WANT the type checking to protect yourself from programming errors. The explicit cast is telling C++ that you KNOW you are doing an unsafe conversion and you promise not to send the enum out of range. That's probably also why things++ is not allowed: the compiler can't be sure the result will be a valid value.

The following code will replace your enum and eliminate all that pesky type checking:

typedef int animal;
#define CAT 1
#define DOG 2
#define Elephant 3
#define Monkey 4