GDI : How to delete a line on right click

    public partial class Form1 : Form
    {
        Boolean drag;
        Point start;
        Point end;

        public Form1()
        {
            InitializeComponent();
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                drag = true;
                start.X = e.X;
                start.Y = e.Y;
            }
            else
            {
                drag = false;

                Graphics g = Graphics.FromHwnd(this.Handle);
                g.Clear(this.BackColor);
            }

            base.OnMouseDown(e);
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            if (drag)
            {
                end.X = e.X;
                end.Y = e.Y;

                Graphics g = Graphics.FromHwnd(this.Handle);

                g.DrawLine(new Pen(Color.Black, 2), start, end);
            }

            base.OnMouseUp(e);
        }
    }


That is a simple answer. If right clicking the form is just suppose to erase the last line drawn then you need to keep track of all the lines that have been drawn. I suggest a generic collection (or better yet a System.Collections.Stack) of a custom structure that contains two System.Drawing.Points. Capture the right click and remove the last line from the collection. Call the Invalidate() method of your form to force a redraw. Overload the OnPaint() method to draw each line in your collection.

you could actually implement eraser for this and draw lines seperately..
you can check here for  a sample on how to do this
http://support.microsoft.com/kb/314945

You actually don't delete a line. You're going to redraw all graphics objects again and this time you are not going redraw the line you want to delete.