Enumerations have the same representation as signed integers and are handy for describing subsets of the integers.
Enumerated data is declared as follows:
enum {name-identifier = constant, ... } identifier;
For example, an enumerated type could represent the three colors red, yellow, and blue as follows:
enum {RED = 2, YELLOW = 3, BLUE = 5} colors;
It is an error to assign to an enum
an integer that has not been assigned in the enum
declaration.
See "Signed Integer".