enum

An enum, short for enumeration, is a user-defined type that consists of a finite set of named constants known as enumerators. It provides a type-safe way to represent a fixed set of values and improves code readability by using meaningful names rather than raw literals. The exact mechanics vary by language.

In many languages, enumerations have an underlying numeric representation. By default, the first enumerator often starts at zero, and subsequent ones increment by one. Some languages allow explicit values and heterogeneous representations, or treat enums as distinct types rather than plain integers.

In C and C++, enums declare a new integral type. Values typically start at zero unless assigned otherwise. C++11 introduced strongly typed scoped enums (enum class) that do not implicitly convert to integers and that restrict scope.

In Java, an enum is a special class type whose instances are the enum constants. Java enums can declare fields, methods, and constructors, and they support iteration and value retrieval with methods such as values() and valueOf.

In C#, an enum is a value type with an underlying numeric type (default int). Underlying types can be specified; the Flags attribute enables bitwise combinations for representing multiple options.

Common uses include modeling states, categories, and options. Enums support comparisons and, in many languages, conversion to and from their numeric or string representations. They contribute to safer interfaces and clearer control flow.