Please see my comment to the question. It's not nice to ask a question and hide the declaration which caused the problem.
Anyway, you just trying to work with some unrelated types, judging by the name
ghMDIClientArea
— very unrelated, by some reason which only you can know. Look at the declaration of
CreateWindow
:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms632679%28v=vs.85%29.aspx[
^].
Return type is
HWND
(window handle), so declare appropriate variable to represent it.
By the way, who needs MDI? This UI style is highly discouraged even by Microsoft. Why torturing yourself and chase out your customers?
—SA