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C# Enum


C#枚举

An enum is a special "class" that represents a group of constants (unchangeable/read-only variables).

To create an enum, use the enum keyword (instead of class or interface), and separate the enum items with a comma:

Example

enum Level 
{
  Low,
  Medium,
  High
}

You can access enum items with the dot syntax:

Level myVar = Level.Medium;
Console.WriteLine(myVar);
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Enum is short for "enumerations", which means "specifically listed".


Enum inside a Class

You can also have an enum inside a class:

Example

class Program
{
  enum Level
  {
    Low,
    Medium,
    High
  }
  static void Main(string[] args)
  {
    Level myVar = Level.Medium;
    Console.WriteLine(myVar);
  }
}

The output will be:

Medium
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Enum Values

By default, the first item of an enum has the value 0. The second has the value 1, and so on.

To get the integer value from an item, you must explicitly convert the item to an int:

Example

enum Months
{
  January,    // 0
  February,   // 1
  March,      // 2
  April,      // 3
  May,        // 4
  June,       // 5
  July        // 6
}

static void Main(string[] args)
{
  int myNum = (int) Months.April;
  Console.WriteLine(myNum);
}

The output will be:

3
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You can also assign your own enum values, and the next items will update the number accordingly:

Example

enum Months
{
  January,    // 0
  February,   // 1
  March=6,    // 6
  April,      // 7
  May,        // 8
  June,       // 9
  July        // 10
}

static void Main(string[] args)
{
  int myNum = (int) Months.April;
  Console.WriteLine(myNum);
}

The output will be:

7
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Enum in a Switch Statement

Enums are often used in switch statements to check for corresponding values:

Example

enum Level 
{
  Low,
  Medium,
  High
}

static void Main(string[] args) 
{
  Level myVar = Level.Medium;
  switch(myVar) 
  {
    case Level.Low:
      Console.WriteLine("Low level");
      break;
    case Level.Medium:
       Console.WriteLine("Medium level");
      break;
    case Level.High:
      Console.WriteLine("High level");
      break;
  }
}

The output will be:

Medium level
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Why And When To Use Enums?

Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.




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