If you size a window larger you will get WM_SIZE and WM_PAINT.
If you size a window smaller, either in the horizontal or Vertical directions, you will get the WM_SIZE, but whether you get the WM_PAINT paint message depends on
how you set the Window Class style setting when you register the window class
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//Step 1: Registering the Window Class
WNDCLASSEX wc;
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_HREDRAW|CS_VREDRAW; //This setting here...