c++ - Enum vs Strongly typed enum

Question

I am a beginner in C++ programming.

Today I come across a new topic: strongly typed enum. I've researched it a bit but till now I am unable to find out why do we need this and what is the use of the same?

For example if we have:

enum xyz{a, b, c};
/*a = 0, b = 1, c = 2, (Typical C format)*/

Why do we need to write:

enum class xyz{a, b, c};

What are we trying to do here? My most important doubt is how to use it. Could you provide a small example, which will make me understand.

Answer 1

OK, first example: old-style enums do not have their own scope:

enum Animals {Bear, Cat, Chicken};
enum Birds {Eagle, Duck, Chicken}; // error! Chicken has already been declared!

enum class Fruits { Apple, Pear, Orange };
enum class Colours { Blue, White, Orange }; // no problem!

Second, they implicitly convert to integral types, which can lead to strange behaviour:

bool b = Bear && Duck; // what?

Finally, you can specify the underlying integral type of C++11 enums:

enum class Foo : char { A, B, C};

Previously, the underlying type was not specified, which could cause compatibility problems between platforms. Edit It has been pointed out in comments that you can also specify the underlying integral type of an "old style" enum in C++11.