Displaying more shapes in the same client Area

Dear Friends
I am a Teacher. At present I face a problem in drawing different shapes in the client area of my window . I am using SDK(WIN32 API).
My problem: Drawing shapes in the client area
1. I select a shape from the menu(resource)
2. I start by dragging the mouse in the client area(the shape keep growing), when I release the mouse the shape will be there.
3. Now I select another shape and drag, the new shape will keep drawing on the client area, but on invalidation the previous shape disappers.
How can I retain the previous shape on invalidating only a particular part.
(I call InvalidateRect() in each WM_MOUSEMOVE with MK_LBUTTON down).
Please provide me a solution soon.
Have a nice day
Bye

Well, being a teacher you undoubtedly appreciate the importance of learning a concept for yourself vice just being presented with a solution. Why don't we begin by posting some specific source code you have written for the task at hand and we will go from there.

Off the top of my head it is apparent that you probably are not saving the client area of your program so that each redrawing simply redraws the client area with the default brush, (WHITE). What needs to happen is that you have a back buffer which is drawn to the front (client area).

Once I see some code I will be glad to answer with some code.

Have a nice day.