Enumeration type

Enumeration type (enumeration) yes C++ A derived data type in , It's a collection of user-defined enumeration constants .

If a variable has only a few possible values , It can be defined as enumeration (enumeration) type . So-called " enumeration " It means to list the values of variables one by one , The value of a variable can only be in the range of listed values .

Create enumeration , Keyword required  enum. The general form of enumeration type is ：

enum  Enum name { 
      identifier [= Integer constant ], 
      identifier [= Integer constant ], 
... 
     identifier [= Integer constant ]
}  Enumerate variables ;

If the enumeration is not initialized , I.e. omit "= Integer constant " when , Start with the first identifier .

for example , The following code defines a color enumeration , Variable c The type of color. Last ,c To be an assignment "blue".

enum color { red, green, blue } c;
c = blue;

By default , The value of the first name is 0, The value of the second name is 1, The value of the third name is 2, And so on . however , You can also assign a special value to the name , Just add an initial value . for example , In the enumeration below ,green  The value of is 5.

enum color { red, green=5, blue };

ad locum ,blue  The value of is 6, Because by default , Each name will be larger than the one before it 1, but red The value of is still 0.