Programming in Objective-C, Fifth Edition

Enumerated Data Types

The Objective-C language enables you to specify a range of values that can be assigned to a variable. An enumerated data type definition is initiated by the keyword enum. Immediately following this keyword is the name of the enumerated data type, followed by a list of identifiers (enclosed in a set of curly braces) that define the permissible values that can be assigned to the type. For example, the following statement defines a data type flag:

enum flag { false, true };

In theory, this data type can be assigned the values true and false inside the program, and no other values. Unfortunately, the Objective-C compiler does not generate warning messages if this rule is violated.

To declare a variable to be of type enum flag ...