C＃|枚举(或枚举)

枚举(或枚举)是C＃中的值数据类型。它主要用于将名称或字符串值分配给整数常量，从而使程序易于阅读和维护。例如，一副扑克牌中的4个西服可以是名为Club，Diamond，Heart和Spade的4个枚举器，属于名为Suit的枚举类型。其他示例包括自然枚举类型(例如行星，星期几，颜色，方向等)。枚举的主要目的是定义我们自己的数据类型(枚举数据类型)。直接在名称空间，类或结构内部使用enum关键字声明枚举。

句法：

enum Enum_variable
{
     string_1...;
     string_2...;
     .
     .
}

在上面的语法中，Enum_variable是枚举数的名称，string_1附加值0，string_2附加值1，依此类推。因为默认情况下，枚举的第一个成员的值为0，并且每个连续的枚举成员的值加1。我们可以更改此默认值。

• 示例1：考虑下面的枚举代码。在这里创建了名称为month的枚举，其数据成员为月份的名称，如jan，feb，mar，apr，may。现在，让我们尝试打印这些枚举的默认整数值。要从枚举类型转换为整数类型，需要显式转换。

  // C# program to illustrate the enums
  // with their default values
  using System;
  namespace ConsoleApplication1 {
    
  // making an enumerator 'month' 
  enum month
  {
    
      // following are the data members
      jan,
      feb,
      mar,
      apr,
      may
    
  }
    
  class Program {
        
      // Main Method
      static void Main(string[] args)
      {
            
          // getting the integer values of data members..
          Console.WriteLine("The value of jan in month " +
                            "enum is " + (int)month.jan);
          Console.WriteLine("The value of feb in month " +
                            "enum is " + (int)month.feb);
          Console.WriteLine("The value of mar in month " +
                            "enum is " + (int)month.mar);
          Console.WriteLine("The value of apr in month " +
                            "enum is " + (int)month.apr);
          Console.WriteLine("The value of may in month " +
                            "enum is " + (int)month.may);
      }
  }
  }
  

  输出：

  The value of jan in month enum is 0
  The value of feb in month enum is 1
  The value of mar in month enum is 2
  The value of apr in month enum is 3
  The value of may in month enum is 4
  

• 示例2：在下面的代码中，将创建带有名称形状的枚举器，并将字符串数据成员设置为Circle ，默认情况下，其初始化为值0，类似地， Square在Perimeter类中分配为值1。还有一个成员函数peri()，它将一个参数作为值来初始化边/半径。另一个参数用于以整数值(0或1)的形式判断形状是圆形还是正方形。现在在main()方法中，创建了Perimeter类的对象。在调用peri()方法期间， Perimeter.shapes.circle表示它是一个值为0的圆，类似的情况是Perimeter.shapes.square的值为1。因此，在方法内部，如果s1对象的值为0那么它是圆形，因此计算出它的周长，正方形也是如此
  周长。

  // C# program to illustrate the Enums
  using System;
  namespace ConsoleApplication2 {
        
  class Perimeter {
        
      // declaring enum 
      public enum shapes 
      {
          circle,
          square
      }
    
      public void peri(int val, shapes s1)
      {
            
          // checking for shape to be circle
          if (s1 == 0) 
          {
                
              // Output the circumference
              Console.WriteLine("Circumference of the circle is " +
                                                    2 * 3.14 * val);
          }
            
          else 
          {
    
              // else output the perimeter of the square
              Console.WriteLine("Perimeter of the square is " + 
                                                       4 * val);
          }
      }
  }
    
  class Program {
        
      // Main Method
      static void Main(string[] args)
      {
    
          Perimeter a1 = new Perimeter();
          a1.peri(3, Perimeter.shapes.circle);
          a1.peri(4, Perimeter.shapes.square);
    
      }
  }
  }
  

  输出：

  Circumference of the circle is 18.84
  Perimeter of the square is 16
  

枚举的初始化：如上所述，第一个枚举成员的默认值设置为0，对于枚举的其他数据成员，其默认值增加1。但是，用户也可以更改这些默认值。

• 例子：

  enum days {
  
        day1 = 1,
  
        day2 = day1 + 1,
  
        day3 = day1 + 2
        .
        .
  
  }
  

  在上面的示例中，day1被用户分配了值“ 1”，day2将被分配了值“ 2”，并且day3成员的情况与此类似。因此，您只需要更改枚举的第一个数据成员的值，枚举的其他数据成员将自动比前一个增加1。

注意：现在，如果enum成员的数据成员尚未初始化，则其值将根据以下规则设置：

• 如果它是第一个成员，则将其值设置为0，否则
• 列出将枚举数据成员的先前值加1所获得的值

• 例子：

  enum random {
  
  A,
  
  B,
  
  C = 6;
  
  D
  
  }
  
  

  在这里，默认情况下A设置为0，B将递增为1。但是，由于C初始化为6，所以D的值为7

• 程序：用用户定义的值演示枚举数据成员的初始化，以及一些特殊的初始化情况。

  // C# program to illustrate the enum 
  // data member Initialisation
  using System;
  namespace ConsoleApplication3 {
        
  // enum declaration
  enum days {
        
      // enum data members
      monday,
      tuesday,
      wednesday,
      thursday,
      friday,
      saturday,
      sunday
  }
    
  // enum declaration
  enum color {
        
      // enum data members
      Red,
      Yellow,
      Blue,
        
      // assigning value yellow(1) + 5
      Green = Yellow + 5,
      Brown,
        
      // assigning value Green(6) + 3
      Black = Green + 3
    
  }
    
  class Program {
        
      // Main Method
      static void Main(string[] args)
      {
    
          Console.WriteLine("Demostrating the difference "+
                        "between Special Initialisation" +
                   "cases and non-initialisation cases\n\n");
    
          // first of all non-initialised enum
          // 'days' will be displayed
          // as mentioned already, the first 
          // member is initialised to 0
          // hence the output will numbers 
          // from 0 1 2 3 4 5 6
    
          Console.WriteLine("Value of Monday is " + 
                                      (int)days.monday);
          Console.WriteLine("Value of Tuesday is " +
                                      (int)days.tuesday);
          Console.WriteLine("Value of Wednesday is " + 
                                      (int)days.wednesday);
          Console.WriteLine("Value of Thursday is " + 
                                      (int)days.thursday);
          Console.WriteLine("Value of Friday is " + 
                                      (int)days.friday);
          Console.WriteLine("Value of Saturday is " + 
                                      (int)days.saturday);
          Console.WriteLine("Value of Sunday is " + 
                                      (int)days.sunday);
    
          // Now the use of special initialisation 
          // cases is demostrated as expected Red 
          // will be assigned 0 value similarily 
          // yellow will be 1 and blue will be 2
          // however, green will be assigned the 
          // value 1+5=6 similarily is the case 
          // with brown and black
    
          Console.WriteLine("\n\nColor Enum");
    
          Console.WriteLine("Value of Red Color is " + 
                                         (int)color.Red);
          Console.WriteLine("Value of Yellow Color is " + 
                                       (int)color.Yellow);
          Console.WriteLine("Value of Blue Color is " + 
                                        (int)color.Blue);
          Console.WriteLine("Value of Green Color is " + 
                                        (int)color.Green);
          Console.WriteLine("Value of Brown Color is " + 
                                        (int)color.Brown);
          Console.WriteLine("Value of Black Color is " + 
                                        (int)color.Black);
      }
  }
  }
  

  输出：

  Demostrating the difference between Special 
  Initialisation cases and non-initialisation cases
  
  
  Value of Monday is 0
  Value of Tuesday is 1
  Value of Wednesday is 2
  Value of Thursday is 3
  Value of Friday is 4
  Value of Saturday is 5
  Value of Sunday is 6
  
  
  Color Enum
  Value of Red Color is 0
  Value of Yellow Color is 1
  Value of Blue Color is 2
  Value of Green Color is 6
  Value of Brown Color is 7
  Value of Black Color is 9
  

  说明：在上面的代码中，我们形成了两种枚举类型，即color和days 。如果是枚举数天，则不会进行初始化。因此，按照规则，星期一将被分配为0，增量为1，将确定星期二，星期三和其他日期的值。但是，在枚举颜色的情况下，红色将被分配0，黄色将被赋值为1，蓝色则被赋值。但是，如果是绿色，则其值将通过将黄色的值与5的值相加来确定，从而得出值6。同样，如果是棕色，则其值为7，如果是黑色，则其值为(7 + 3)是10。

更改Enum数据成员的类型：默认情况下，C＃中枚举器的基本数据类型为int 。但是，用户可以根据需要更改它，例如bool，long，double等。

• 例子：

  // byte type
  enum button : byte {
  
  // OFF will be assigned 0
  OFF,
  
  //ON will be assigned 1
  ON
  
  // However, if we assign 100 to ON then, 
  // this will give error as byte cannot hold this
  
  }
  

• 程序：演示枚举成员数据类型的更改

  // C# program to illustrate the changing 
  // of data type of enum members
  using System;
  namespace ConsoleApplication4 {
    
  // changing the type to byte using :
  enum Button : byte {
        
      // OFF denotes the Button is 
      // switched Off... with value 0
      OFF,
    
      // ON denotes the Button is 
      // switched on.. with value 1
      ON
    
  }
    
  class Program {
        
      // Main Method
      static void Main(string[] args)
      {
    
          Console.WriteLine("Enter 0 or 1 to know the " + 
                         "state of electric switch!");
    
          byte i = Convert.ToByte(Console.ReadLine());
    
          if (i == (byte)Button.OFF)
          {
    
              Console.WriteLine("The electric switch is Off");
          }
            
          else if (i == (byte)Button.ON) 
          {
              Console.WriteLine("The electric switch is ON");
          }
            
          else
          {
              Console.WriteLine("byte cannot hold such" + 
                                        " large value");
          }
      }
  }
  }
  

  输入：

  1

  输出：

  Enter 0 or 1 to know the state of electric switch!
  The electric switch is ON