problem closing a window

I have a program with two windows. I open the second window by pressing a button. And close it using the DestroyWindow( ), I also tried PostQuitMessage(WM_QUIT ). Both of these functions result in the program crashing. When I click on the X in the top right of the window or press alt+F4 the window closes perfectly and returns to the first window.

Q. What signal is alt+F4 sending to the window.



p.s I am using VC++

>>Q. What signal is alt+F4 sending to the window.<<

A. WM_SYSCOMMAND.

For future reference you should direct your windows questions to the windows board.

WM_CLOSE
this may be what you are after