枚举

public enum TimeOfDay{
  Morning = 0,
  Afternoon = 1,
  Evening = 2
}

class EnumExample{
  public Static int Main(){
    WriteGreeting(TimeOfDay.Morning);
    return 0;
  }
  static void WriteGreeting(TimeOfDay timeOfDay){
    switch(timeOfDay){
      case TimeOfDay.Morning:
        Console.WriteLine("Good morning!");
        break;
      case TimeOfDay.Afternoon:
        Console.WriteLine("Good afternoon!");
        break;
      case TimeOfDay.Evening:
        Console.WriteLine("Good evening!");
        break;
      default:
        Console.WriteLine("Hello!");
        break;
    }
  }
}

TimeOfDay time = TimeOfDay.Afternoon;
Console.WriteLine(time.ToString());