enum keyword

enum

The enum keyword is used when you require a enumeration. A enumeration is a distinct type that consists of a set of named constants called the enumetor list. Every enumeration type has an underlying type which can be all integral times except that of a char type.

Declaration syntax:

[attributes] [modifiers] enum identifier [:base-type] {enumerator-list};

Where:

attributes (optional) - this is additional declarative information, look under index A for more information
modifiers (optional) - permissible modifiers include: new, public, protected, internal and private ( the 4 access modifiers)
base-type (optional) - underlying type for the storage allocated for each enumerator, any integral type except char (default is int)
enumerator-list - the enumerators identifiers which are seperated by commas (optionally including a value assignment)

Key Points:

The default underlying type of the elements in the enumeration is int as previously mentioned. The first enumerator begins at 0 by default and each enumerator following is increased by 1. Explicit casts are required to convert from enum type to an integral type.

Examples:

// create enum for all of the months in a year
enum Months {Jan, Feb, March, April,
	 May, June, July, August, Sept, Oct, Nov, Dec};

// same as above EXCEPT forced to start sequence 
// from 1 instead of 0 (default)
enum Months2 {Jan = 1, Feb, March, April,
	 May, June, July, August, Sept, Oct, Nov, Dec};
    
public void Page_Load(object sender, EventArgs e)
{
    // notice the explicit cast required
    int x = (int) Months.Feb;
    int y = (int) Months.Oct;
    
    Response.Write("
Feb is month #" + x);
    Response.Write("
Oct is month #" + y);
    
    // sequence forced to start with 1 i.e Jan = 1 (in the declaration)
    x = (int) Months2.Feb;
    y = (int) Months2.Oct;
    
    Response.Write("
Feb is now month #" + x);
    Response.Write("
Oct is now month #" + y);
    

}