I read chapter 19 for Chalres Petzold Book (Windows Programming)..
This chapter explain how to create Multi Document interface (MDI)..

But after reading this chapter I was confused for Window Class ...
I will expalin in simple words ..
for MDI we have to create two windows
first Window is : Frame Window (= Main window of program)
second Window: Child Window

Petzold in his book Created only one window Class Say = WndClass
He Used This class one time to Prepare Frame Window ; Second time He Used the same class to prepare Child Window

the code for frame Window is :

wndclass.lpfnWndProc = FrameWndProc ;
....................
...............


the code for Child Window is :
wndclass.lpfnWndProc = HelloWndProc ;
........................
.............................


My Questions are :

Q1:
should the application have only one Window Class ?? and this will be used for all windows of the program,

Or I can Use many Window Classes in the same Program ?? and Why...

Q2:
and here , Petzold used the same Window class , How I can store the data two times .. I stored the data for wndclass when I create Frame Window
and Again I store the new data for the same Class when I create The Child Window!!!?? or something is not clear with Me??

Thanks & Regards