Scaling child elements of a Windows window?

Question

C++ / C#

How to make that when the window is resized, its child elements (buttons, windows, etc.) would change proportionally. Most likely, this is some property of the main application window itself, but what is it? Couldn't find an answer on google. On MSDN too.
Source code:
pastebin.com/1ZujQKrA
Before scaling:

After scaling:

Answer 1

C++ is not Delphi, there will be no freebies. You need to handle the WM_SIZE message yourself in MainWndProc . With the parameters, everything is simple (link) and then - with handles.

Answer 2

Offhand, it only comes to mind to handle OnResize.