An application can allow Windows to calculate the initial size or position of a top-level window by specifying CW_USEDEFAULT in CreateWindowEx. If the application sets the window's coordinates to CW_USEDEFAULT and has created no other top-level windows, Windows sets the new window's position relative to the upper left corner of the screen; otherwise, it sets the position relative to the position of the top-level window that the application created most recently. If the width and height parameters are set to CW_USEDEFAULT, Windows calculates the size of the new window. If the application has created other top-level windows, Windows bases the size of the new window on the size of the application's most recently created top-level window. Specifying CW_USEDEFAULT when creating a child or pop-up window causes Windows to set the window's size to the default minimum window size.