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Importing DLL in .NET

The following example shows how a DLL can be imported and called in c sharp. It calls MessageBeep (which is a Win32 API function). MessageBeep is found in user32.dll. 
using System;

using System.Runtime.InteropServices;

class ImportDll {

  static void Main() {
    MessageBeep(BeepType.IconExclamation);
  }
  
  [DllImport("user32.dll")]
  public static extern bool MessageBeep(BeepType beepType);
  
  public enum BeepType {
      SimpleBeep      = -1,
      IconAsterisk    = 0x00000040,
      IconExclamation = 0x00000030,
      IconHand        = 0x00000010,
      IconQuestion    = 0x00000020,
      OK              = 0x00000000
  }
}