C# Tutorial - Application 11 – Enumerating Constants

When you have a group of related constants, you may wish to combine them into an enumeration. An enumeration is a value type defined at compile time that groups related constants. All of the constants must be of the same type.

Create a new console Application called App11. We are going to create a simple application that displays the contents of an enumeration. Add the following code:

class Program
{
  enum Marks
  {
    Pass = 40,
    Merit = 65,
    Distinction = 85
  }

  static void Main(string[] args)
  {
    Console.WriteLine("The {0} mark is {1}", Marks.Pass,
       (int)Marks.Pass);

    Console.WriteLine("The {0} mark is {1}", Marks.Merit,
       (int)Marks.Merit);

    Console.WriteLine("The {0} mark is {1}", Marks.Distinction,
       (int)Marks.Distinction);
  }
}

Which gives the output:

The Pass mark is 40
The Merit mark is 65
The Distinction mark is 85

We accessed the enumeration Marks twice in each WriteLine statement.

  • Firstly, to get the name of the constant, we called each constant within the enumeration on its own.

  • Secondly, to get the associated value of the constant, we called each constant within the enumeration and cast it to an integer value.

We could, if we wanted to, compare a number with the associated value of any of the constants. For example:

if( _assignment < (int)Marks.Pass )
  Console.WriteLine("You failed the assignment");
else
  Console.WriteLine("You passed the assignment");

Enumerations

An enumeration contains a related group of constants of the same type, which must be byte, sbyte, short, ushort, int, uint, long or ulong. An enumeration takes the following form:

enum-modifiers enum identifier : enum-base
{
  enum-body
}

Where:

  • The enum-modifiers is optional any contain a valid combination of any of the following:

    • new
    • public
    • protected
    • internal
    • private

  • The identifier is name of the enumeration.

  • The enum-base is optional. It details the base type from which the enumeration derives and must be one of the types listed above. When it is not used, the enum-base defaults to int.

  • The enum-body consists of the constant values.

When declaring an enumeration, if you do not assign any values to the constants, then they will automatically be assigned values starting at zero and incrementing by one for each constant. Similarly if you give the first constant a value, then each constant thereafter will increment by one. In the following example, Spring is assigned the value 1 and the other values become those shown in the comments.

enum Seasons
{
  Spring = 1,
  Summer,     // 2
  Autumn,     // 3
  Winter      // 4
}

When using an enumeration, you must call the enumeration before the element of the enumeration that you require. This is because the constants are contained within the scope of the enumeration and mean nothing outside of it on their own. This allows different enumerations to contain the same names without naming collisions.

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© Publicjoe, 2008