# Enums

An enumeration is a distinct type whose value is restricted to a specific range or list of values, which may include several explicitly named constants. The values of the constants are values of an integral type known as the underlying type of the enumeration.

Enums are used to assign names to the integral constants which makes a program easy to read and maintain.

# Defining an Enumeration

An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, the keyword enum is used.

enum DayOfTheWeek {
  MONDAY,
  TUESDAY,
  WEDNESDAY,
  THURSDAY,
  FRIDAY,
  SATERDAY,
  SUNDAY
};

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The enumerator labels are automatically assigned an integral value starting from 0. So the label SUNDAY will have a value of 6.

To declare a variabel of the enum type, use the defined type as any other data type:

DayOfTheWeek today = WEDNESDAY;
cout << "Today we are the " << today << "th day of the week." << endl;

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Output

Today we are the 2th day of the week.

# Renumbering an Enum

By default, the first element in an enum is assigned 0, the second 1 and so on. These default values can be changed during declaration if needed.

enum DayOfTheWeek {
  MONDAY = 1,
  TUESDAY,
  WEDNESDAY,
  THURSDAY,
  FRIDAY,
  SATERDAY,
  SUNDAY
};

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If successive labels are not assigned a value manually, a value is automatically assigned starting by incrementing the previous value.

Another example:

enum Season {
  SPRING = 3,
  SUMMER = 6,
  AUTUMN = 9,
  WINTER = 12
};

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# Scoped Enums

In the original C and C++ enum types, the unqualified enumerators are visible throughout the scope in which the enum is declared. In scoped enums, the enumerator name must be qualified by the enum type name.

enum class Suit { DIAMONDS, HEARTS, CLUBS, SPADES };

Notice that the class keyword follows the enum keyword to create a scoped enum.

Now the type of the enum needs to be specified when using the enum labels:

Suit cardSuit = Suit::HEARTS;

This prevents collisions and also makes code more clear.

# Enums for Flags

Enums are often used when flags need to be passed to a function. Instead of passing a variable for each flag, the flags are combined using an enum where the values are powers of two.

Example:

enum class Style {
  ITALIC = 1,
  BOLD = 2,
  UNDERLINED = 4,
  STRIKETHROUGH = 8
};

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By casting the Style values to int, different Style values can be combined using the bitwise OR operator as shown in the next example.

// Possible styles
enum class Style {
  ITALIC = 1,
  BOLD = 2,
  UNDERLINED = 4,
  STRIKETHROUGH = 8
};

// Combining some styles
int heading = (int)(Style::BOLD) | (int)(Style::UNDERLINED);

// What styles were selected ?
if (heading & (int)Style::ITALIC) std::cout << "Style is italic" << std::endl;
if (heading & (int)Style::BOLD) std::cout << "Style is bold" << std::endl;
if (heading & (int)Style::UNDERLINED) std::cout << "Style is underlined" << std::endl;
if (heading & (int)Style::STRIKETHROUGH) std::cout << "Style is strikethrough" << std::endl;

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Output

Style is bold
Style is underlined

# Exercises

Try to solve the exercises yourself. Don't go copy pasting other people's solutions.

Mark the exercises using a ✅ once they are finished.

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