How to change the System Volume programmatically

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C#

I want to change the System's Volume. I am using following code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace shaped_form
{
class VolumeChange
{
private const int APPCOMMAND_VOLUME_MUTE = 0x80000;
private const int APPCOMMAND_VOLUME_UP = 0xA0000;
private const int APPCOMMAND_VOLUME_DOWN = 0x90000;
private const int WM_APPCOMMAND = 0x319;
[DllImport("user32.dll")]
public static extern IntPtr SendMessageW(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);
private void btnMute_Click(object sender, EventArgs e)
{
SendMessageW(this.Handle, WM_APPCOMMAND, this.Handle,(IntPtr)APPCOMMAND_VOLUME_MUTE);
}
private void btnDecVol_Click(object sender, EventArgs e)
{
SendMessageW(this.Handle, WM_APPCOMMAND, this.Handle,(IntPtr)APPCOMMAND_VOLUME_DOWN);
}
private void btnIncVol_Click(object sender, EventArgs e)
{
SendMessageW(this.Handle, WM_APPCOMMAND,this.Handle,(IntPtr)APPCOMMAND_VOLUME_UP);
}
}
}

But I got an error at the highlighted places as "shaped_form.VolumeChange does not contain a definition for Handle". I got this code from some internet sources.
and also please tell me about Intptr and it's importance here.