An enumeration is a data type that enumerates a set of items by assigning to each of them an identifier (a name), while exposing an underlying base type for ordering the elements of the enumeration. The underlying type is int by default, but can be any one of the integral types except for char.

Enumerations are declared as follows:

enum Weekday { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday };
                                          

The elements in the above enumeration are then available as constants:

Weekday day = Weekday.Monday;
if (day == Weekday.Tuesday)
{
    Console.WriteLine("Time sure flies by when you program in C#!");
}
                                          

If no explicit values are assigned to the enumerated items as the example above, the first element has the value 0, and the successive values are assigned to each subsequent element. However, specific values from the underlying integral type can be assigned to any of the enumerated elements:

enum Age { Infant = 0, Teenager = 13, Adult = 18 };

Age age = Age.Teenager;
Console.WriteLine("You become a teenager at an age of {0}.", age.ToString());
                                          

The underlying values of enumerated elements may go unused when the purpose of an enumeration is simply to group a set of items together, e.g., to represent a nation, state, or geographical territory in a more meaningful way than an integer could. Rather than define a group of logically related constants, it is often more readable to use an enumeration.

It may be desirable to create an enumeration with a base type other than int. To do so, specify any integral type besides char as with base class extension syntax after the name of the enumeration, as follows:

enum CardSuit : byte { Hearts, Diamonds, Spades, Clubs };
                                          

All text is available under the terms of the GNU Free Documentation License
Source : Wikibooks