Enumerations

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1. What is an enumeration in C#?

Enumerations in C# are a set (sequence) of constants that form a data type. The value of each constant is given by a name. In C#, enumerations are represented by a class. All enums are inherited from the System.Enum class.

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2. What is the general form of an “enumeration” type? The enum keyword

The general form of the declaration of type “enumeration” is:

enum name { list_of_constants };

where

name – this is the name of the enumeration type;
list_of_constants – a list of identifiers, separated by commas.

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3. In parts of the program can you declare the type of “enumeration”

The “enum” type can be declared within the namespace within the class. In the body of the method, it is not possible to declare the type of an enumeration.

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4. Examples of declaring the enumerations and their use in the program

Example 1. The Month declaration that defines the list of months of the year.

// Declare type "Month"
enum Month
{
    January, February, March, April, May, June,
    July, August, September, October, November, December
}

Using the Month type in another code (for example, an event handler)

// use of enumeration in the program code
Month M; // Declaring an M variable of type "enumeration"

M = Month.January; // M = January

int m;
m = (int)M; // m = 0

M = Month.August; // M = August
m = (int)M; // m = 7

Example 2.

A DayWeek type declaration containing information about the day of the week.

enum DayWeek
{
    Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
}

An example of using composite assignment operators with a variable of type DayWeek:

DayWeek D;

D = DayWeek.Sunday;

D++; // D = Monday
D += 2; // D = Wednesday
D += 10; // D = 13

D = DayWeek.Friday;
--D; // D = Thursday
D = D - 8; // D = -4

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5. How is the enumeration initialized? Example

Example 1. Initializing an enumeration of the Month type, in which each month is initialized with a value equal to the number of days in this month.

Declaring of enumeration:

// Declare the 'Month' type
enum Month
{
    January = 31, February = 28, March = 31, April = 30, May, June = 30,
    July, August = 31, September = 30, October, November = 30, December
}

Demonstration of using a variable of type Month

Month M;
int days;

M = Month.December; //
days = (int)M; // days = 31

M = Month.October;
days = (int)M; // days = 31

M = Month.February;
days = (int)M; // days = 28

Example 2. Declaration of the enumeration, in which the day of the week has its number starting on Monday. A rule is shown: each next constant is assigned a value that is 1 greater than the value of the previous initialized constant.

Declaring a DayWeek type enumeration

enum DayWeek
{
    Sunday = 7, Monday = 1, Tuesday, Wednesday, Thursday, Friday, Saturday
}

Demonstration of use in the program

DayWeek DW; // variable of type DayWeek

DW = DayWeek.Saturday;

// Determining whether a day off or working day
if ((DayWeek.Monday <= DW) && (DW <= DayWeek.Friday))
    label1.Text = "Working day";
else
    label1.Text = "Day off";

DW = DayWeek.Thursday;
int num = (int)DW; // num = 4
num = (int)DayWeek.Tuesday; // num = 2

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6. Which basic type have constants in the enumeration by default?

By default, the base type for constants in the enumeration is int.

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7. How can I change the basic type of constants in the enumeration?

To change the base type of constants from int to another, you must specify this type immediately after the name of the enumeration. The general form of such enumeration will look like:

enum name : new_type { list_of_constants };

where

name – this is the name of the enumeration type;
new_type – in fact, a new type that is installed in place of the base type;
list_of_constants – a list of identifiers, separated by commas.

Example. A type declaration is given that defines the grades in the disciplines. In the enumeration declaration, the constants are of type byte.

enum Marks : byte
{
    unsatisfactory = 2, satisfactory, good, excellent
}

Using a Marks variable in the program

Marks M;
M = Marks.good;
byte b;

b = (byte)M; // b = 4
b = (byte)Marks.excellent; // b = 5

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8. What are the advantages of using enumerations in the programs?

The use of enumerations is effective if the program often uses constants that have symbolic designations. Using enumerations instead of numeric values has the following advantages:

increasing understanding and readability of program code, since the reference is not to numbers, but to semantic names;
improving control over the validity of names and their values. Using enumerations ensures that variables will have values from the expected (valid) set of values. If you try to assign a value not declared in the enumeration, the compiler will throw an error;
saving programmer time. When using names, IntelliSense displays a convenient list of all valid names in an enumeration. Simply select the desired value from the list;
expansion of functionality. Since enumerations are inherited from the System.Enum class, several useful methods implemented in this class are added to them;
reducing the number of possible errors in the program.

Also, the use of enumerations allows group the constants in order to further operate them. This, in turn, streamlines the program code and reduces the risk of making a mistake by the programmer.

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9. An example of using an enumeration with a switch statement

The example uses the Month enumeration to determine the number of days in a month.

Let the ‘Month’ enumeration declarations are given

// declare the Month type
enum Month
{
    January, February, March, April, May, June,
    July, August, September, October, November, December
}

Using a variable of type ‘Month’ in the program

// Determining the number of days in a month
Month M;
int n_days;

M = Month.November;

switch (M)
{
    case Month.February: n_days = 28;
    break;

    case Month.April:
    case Month.June:
    case Month.September:
    case Month.November: n_days = 30;
    break;

    default: n_days = 31;
    break;
}

// display to the form
label1.Text = n_days.ToString();

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C#. Enumerations