Windows Form Automation in C++ using low level WinAPI Calls?

I am working on a project that is supposed to take a program written in C++ using Windows forms (a basic calculator taking two ints, an operator and has an equals button) and automates it using C++ and low level WinAPI calls.

I have been googling a bit, but most of the references I find on this are fairly old and I want to make sure I'm going in the right direction. I see OLE Automation but not sure if that's the right direction

What I do know: I cannot use Reflection, any 3rd party library including Visual Studio's UI/Testing automation assemblies.

I assume whatever I use I will launch the application, get the window by it's title, get each element by the element name somehow, simulate a click, read the calculated value, etc. It's just getting there that is the problem