title: The lparam and wparam parameters in this specific sendmessage function?
body: <p>I was going through this code <a href="http://social.msdn.microsoft.com/Forums/vstudio/en-US/8308f020-b9e6-472c-aaac-93619a8a5a7d/vbnet-control-the-system-volume-mute-and-output-the-current-level-to-the-user?forum=vbgeneral" rel="nofollow">here</a> and:</p>
  
  <pre><code> Private Sub Button3_Click(ByVal sender As System.Object, 
          ByVal e As System.EventArgs) Handles Button3.Click
        SendMessage(Me.Handle, WM_APPCOMMAND, &amp;H200EB0, 
                     APPCOMMAND_VOLUME_MUTE * &amp;H10000)
      End Sub
  </code></pre>
  
  <p>I have no idea what the last two parameters of the sendmessage functions are and what is going on in these two parameters? the "&amp;H200EB0" and "APPCOMMAND_VOLUME_MUTE * &amp;H10000" Parameters?</p>
  
  <p>Here's the full code:</p>
  
  <pre><code>    Imports System.Runtime.InteropServices
  Public Class Form1
      &lt;DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)&gt; 
      Private Shared Function SendMessage(ByVal hWnd As IntPtr, 
                      ByVal Msg As UInteger, ByVal wParam As IntPtr, 
                      ByVal lParam As IntPtr) As IntPtr
      End Function
  
      Const WM_APPCOMMAND As UInteger = &amp;H319
      Const APPCOMMAND_VOLUME_UP As UInteger = &amp;HA
      Const APPCOMMAND_VOLUME_DOWN As UInteger = &amp;H9
      Const APPCOMMAND_VOLUME_MUTE As UInteger = &amp;H8
  
      Private Sub Button1_Click(ByVal sender As System.Object, 
               ByVal e As System.EventArgs) Handles Button1.Click
          SendMessage(Me.Handle, WM_APPCOMMAND, &amp;H30292, 
                      APPCOMMAND_VOLUME_UP * &amp;H10000)
      End Sub
  
      Private Sub Button2_Click(ByVal sender As System.Object, 
                   ByVal e As System.EventArgs) Handles Button2.Click
          SendMessage(Me.Handle, WM_APPCOMMAND, &amp;H30292, 
                      APPCOMMAND_VOLUME_DOWN * &amp;H10000)
      End Sub
  
      Private Sub Button3_Click(ByVal sender As System.Object, 
             ByVal e As System.EventArgs) Handles Button3.Click
          SendMessage(Me.Handle, WM_APPCOMMAND, &amp;H200EB0, 
                      APPCOMMAND_VOLUME_MUTE * &amp;H10000)
      End Sub
  End Class
  </code></pre>