Книга: C# 2008 Programmer

Enumerations

Enumerations

You can create your own set of named constants by using enumerations. In C#, you define an enumeration by using the enum keyword. For example, say that you need a variable to store the day of a week (Monday, Tuesday, Wednesday, and so on):

static void Main(string[] args) {
 int day = 1; //--- 1 to represent Monday---
 //...
 Console.ReadLine();
 return;
}

In this case, rather than use a number to represent the day of a week, it would be better if the user could choose from a list of possible named values representing the days in a week. The following code example declares an enumeration called Days that comprises seven names (Sun, Mon, Tue, and so forth). Each name has a value assigned (Sun is 0, Mon is 1, and so on):

namespace HelloWorld {
 public enum Days {
  Sun = 0,
  Mon = 1,
  Tue = 2,
  Wed = 3,
  Thur = 4,
  Fri = 5,
  Sat = 6
 }
 class Program {
  static void Main(string[] args) {
   Days day = Days.Mon;
   Console.WriteLine(day); //---Mon---
   Console.WriteLine((int) day); //---1---
   Console.ReadLine();
   return;
  }
 }
}

Instead of representing the day of a week using an int variable, you can create a variable of type Days. Visual Studio 2008's IntelliSense automatically displays the list of allowed values in the Days enumeration (see Figure 3-9).


Figure 3-9

By default, the first value in an enumerated type is zero. However, you can specify a different initial value, such as:

public enum Ranking {
 First = 100,
 Second = 50,
 Third = 25
}

To print out the value of an enumerated type, you can use the ToString() method to print out its name, or typecast the enumerated type to int to obtain its value:

Console.WriteLine(day); //---Mon---
Console.WriteLine(day.ToString()); //---Mon---
Console.WriteLine((int)day); //---1--- 

For assigning a value to an enumerated type, you can either use the name directly or typecast the value to the enumerated type:

Days day;
day = (Days)3; //---Wed---
day = Days.Wed; //---Wed--- 

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