enum

enum Direction {
    UP,
    LEFT,
    DOWN,
    RIGHT
};
Direction d = UP;

In C++11, enum may optionally be followed by class or struct to define a scoped enum. Furthermore, both scoped and non-scoped enums can have their underlying type explicitly specified by : T following the enum name, where T refers to an integer type.

enum class Format : char {
    TEXT,
    PDF,
    OTHER
};
Format f = Format::TEXT;

enum Language : int {
    ENGLISH,
    FRENCH,
    OTHER
};

Enumerators in normal enums may also be preceded by the scope operator, although they are still considered to be in the scope the enum was defined in.

Language l1, l2;

l1 = ENGLISH;
l2 = Language::OTHER;

An enum first declared as scoped cannot later be declared as unscoped, or vice versa. All declarations of an enum must agree in underlying type.

When forward-declaring an unscoped enum, the underlying type must be explicitly specified, since it cannot be inferred until the values of the enumerators are known.

enum class Format; // underlying type is implicitly int
void f(Format f);
enum class Format {
    TEXT,
    PDF,
    OTHER,
};

enum Direction;    // ill-formed; must specify underlying type