You can program in Windows without using WinAPI (or rather, with very limited API usage) if you use MFC (or OWL if you're a Borland guy). It's a very good idea to learn straight WinAPI, but it doesn't make much sense to use it for everything. For rapid development, MFC can make Visual C++ very quick, I'm talking fully-featured GUI programs in a few hours.
Originally posted by DougDbug
I assume that by "Vsual C++", you're talking about Windows programs. This means learning the Windows API. There is a lot to learning the WinAPI, and it wouldn't hurt to start now. Charles Petzold's book "Programing Windows" is generally considered the best book on the subject. He concentrates on the Windows API functions. There are no complicated algorithms... In fact, he only uses C (not C++).
Personally, I'd hold-off on the C#. I expect that there will be limited acceptance of this proprietary (Microsoft-Only) language... Only my opinion... and I'm not a Microsoft hater!
From what I hear, Visual Basic (which unlike Visual C++, actually is a language) is extremely popular in the "real world". And, it is apparently much easier than using C/C++ to create Windows applications. My boss uses it. I've never learned it. But, maybe CornedBee is right... maybe it's past it's peak. (?)
Any of your ideas would be worthwhile. So, pick something you would like to do and enjoy your summer!