Thread: getting the size of the window

i started with the main window and i simply want to place a pushbutton at the bottom left hand corner of the window. and i was going to use a function to get the width/length of the window (NOT the screen) so i can calculate exactly where i want the button to be placed instead of using just hard coded numbers (pixel values).

i know of GetSystemMetrics(SM_CXSCREEN) and GetSystemMetrics(SM_CYSCREEN) to get the total width and length of the entire screen, but i just want the width and lenght of the main window i'm working on.

is there a function to do this? if so how is it implemented?

thanks.