You can buy either one. Doesn't make a difference but..
There is a difference in what program that you use for C++. For Windows I use Dev C++. If I were to use a MAC. I would use Eclipse for C++ programmers. But there also is a difference in how these work for different operating systems.
For Windows based PCs, you have to include -- system("pause"); -- which has your code pause so that you can read it. I don't know what to do for MAC but it can't be much different.
Ultimately it's your choice. The differences aren't too big.
I really liked Netbeans as an IDE. Its intellisense-like features are very good and it offers some support for Qt application building. The only immediately obvious downside that I see is that I think you'd need to also download MinGW with it, preferably before, which really isn't a bigie.
I've heard good things about Visual Studio 2010 Express, but I cannot verify any of it. :)
You can program in C++ in whatever you buy so I would make your choice for other reasons.
I think most people will be happiest with a Windows laptop, because that's what most other people have and that runs the same software that most other people run.
Personally I hate Windows and avoid it like the plague.
If you are really looking for a "programmer's" system then I would consider Linux, rather than a Mac, but you should try out these other Operating Systems before you spend lots of money on something you really don't like.
BTW, its not strictly "Mac vs PC". It is "Mac PC vs Windows PC".
PC simply means Personal Computer and it can be Mac, Windows, Linux or otherwise. The pervasiveness of Windows PCs has lead to some people associating the term PC only with Windows.
If you do decide to go with Linux, then two distributions I recommend for getting your feet wet are Linux Mint and Ubuntu.
Ubuntu is probably the largest Linux distribution and I remember it used to be fairly solid as far as stability goes. Unfortunately, I find that Ubuntu's stability had dropped from the 11.04 version onward... I'm not 100% sure why, but my guess is that it has something to do with their radically changed new interface.
I don't know much about Linux Mint's stability, as it is a Ubuntu derivative but they might have patched a few bugs. However, its interface is much easier to use if you're coming from a Windows background than Ubuntu's. Right now, I think I'd recommend this one over Ubuntu.*
*This may not matter to some people, but IMO I also think it's prettier.
I program on Windows. I wouldn't know any reason why it would be better than any other OS for programming; I'm just a Windows "fan" (I value Windows' flexibility/compatibility over iOS' "oo shiny" and quite frankly my Windows has never "randomly crashed" to motivate a switch to linux. I do plan on messing around with linux when my personal system gets a bit too old for gaming.).
Microsoft Visual C++ 2010 Express is very nice (I prefer it over Codeblocks, Eclipse and Netbeans, but I've only used those last two for Java. The C++ experience might be different). I've also had the luxury of using the Visual Studio 2010 Professional and Ultimate editions, but they have far more features than I need. The only thing I really need is the Profiler that comes with it.
Comparison-wise, this post won't help you much, as I've never programmed on an iOS or linux environment. However, you shouldn't rule out Windows. In my opinion, it's the "perfect" mix of flexibility and user-friendliness (but I suppose linux has improved drastically in that last category as well).
Gaminic, iOS is used on iPhones, iPads, iPods. I think you probably mean Mac OS.
For me, if you want to program for Mac, Windows, and Linux then a Mac is the only choice for a single system solution (you are not legally going to be able to run Mac OS on hardware other than Apples). I personally find Macs the most versatile platform to work on.