C Pocket Reference

Enumeration Types

Enumeration types are used to define variables that can only be assigned certain discrete integer values throughout the program. The possible values and names for them are defined in an enumeration. The type specifier begins with the keyword enum ; for example:

enum toggle { OFF, ON, NO = 0, YES };

The list of enumerators inside the braces defines the new enumeration type. The identifier toggle is the tag of this enumeration. This enumeration defines the identifiers in the list (OFF, ON, NO, and YES) as constants with type int.

The value of each identifier in the list may be determined explicitly, as in NO = 0 in the example above. Identifiers for which no explicit value is specified are assigned a value automatically based on their position in the list, as follows: An enumerator without an explicit value has the value 0 if it is the first in the list; otherwise its value is 1 greater than that of the preceding enumerator. Thus in the example above, the constants OFF and NO have the value 0, while ON and YES have the value 1.

Once an enumeration type has been defined, variables with the type can be declared within its scope. For example:

enum toggle t1, t2 = ON;

This declaration defines t1 and t2 as variables with type enum toggle, and also initializes t2 with the value ON, or 1.

Following is an enumeration without a tag:

enum { black, blue, green, cyan, red, magenta, white };

As this example illustrates, the definition of an enumeration does not necessarily include ...