1:  

   2:   enum Animal

   3:   {

   4:       Dog = 0x0001,

   5:       Cat = 0x0002,

   6:       Duck = 0x0004,

   7:       Chicken = 0x0008

   8:   }

   9:   static void Main(string[] args)

  10:   {

  11:       Animal animals = Animal.Dog | Animal.Cat;

  12:       Console.WriteLine(animals.ToString());

  13:       Console.ReadKey();

  14:   }

   1: [Flags]

   2: enum Animal

   3: {

   4:     Dog = 0x0001,

   5:     Cat = 0x0002,

   6:     Duck = 0x0004,

   7:     Chicken = 0x0008

   8: }

   9: static void Main(string[] args)

  10: {

  11:     Animal animals = Animal.Dog | Animal.Cat;

  12:     Console.WriteLine(animals.ToString());

  13:     Console.ReadKey();

  14: }

   1: using System.Runtime.InteropServices;

   2:  

   3: namespace WindowsFormsApp1

   4: {

   5:     public partial class Form1 : Form

   6:     {

   7:         public Form1()

   8:         {

   9:             InitializeComponent();

  10:         }

  11:         [DllImport("User32.dll")]

  12:         public static extern int MessageBox(int hParent, string msg, string caption, int type);

  13:  

  14:  

  15:         private void button1_Click(object sender, EventArgs e)

  16:         {

  17:             MessageBox(0, "How to use attribute in .NET", "User32.dll", 0);

  18:         }

  19:     }

  20: }