Enums

An enum (enumeration) is a user-defined data type that represents a set of named integral constants.

Instead of:

int status = 2; // what is 2?

We write:

Status status = SUCCESS; // readable

Basic Syntax (Classic enum)

enum EnumName {
    CONSTANT1,
    CONSTANT2,
    CONSTANT3
};

// Example:
enum Color {
    RED,        // By default: RED = 0
    GREEN,      // By default: GREEN = 1
    BLUE        // By default: BLUE = 2
};

Using an enum:

Color c = RED;

if (c == GREEN) {
    // do something
}

Assigning Custom Values:

enum ErrorCode {
    OK = 0,
    NOT_FOUND = 404,
    SERVER_ERROR = 500
};

1. Values must be integral constants

2. Unassigned values continue incrementing

enum day {mon, tue, wed, thu, fri, sat, sun};
           0    1    2    3    4    5    6

enum day {mon = 1, tue, wed, thu, fri, sat, sun};
                    2    3    4    5    6    7

enum day {mon = 1, tue, wed = 5, thu, fri, sa = 9, sun};
                    2             6    7           10

3. Enum names go into the same scope (classic enum)

enum Color { RED, GREEN };
enum Traffic { GREEN, YELLOW }; // ❌ conflict

Classic enums pollute the namespace. This is why modern C++ fixed it.

Scoped Enums

enum class Color {
    RED,
    GREEN,
    BLUE
};

// Usage:
Color c = Color::RED;

Why enum class is better:

enum	enum class
Implicit int conversion	No implicit conversion
Pollutes scope	Scoped
Less type-safe	Strongly typed

Last modified: 08 February 2026