A code instance that USES C to draw on the screen

The following C# code implements the ability to draw pictures on the screen! The specific code is as follows:

//DllImport The name space 
 using System.Runtime.InteropServices;
[DllImport("User32.dll")]
public extern static System.IntPtr GetDC(System.IntPtr hWnd);  
private void button19_Click(object sender, EventArgs e)
{
    System.IntPtr    DesktopHandle   =    GetDC(System.IntPtr.Zero);
    Graphics g = Graphics.FromHdc(DesktopHandle);
    g.DrawRectangle(new Pen(Color.Red),new Rectangle(10,10,100,100));
}