You can program in C for OS X. There's the Carbon API which is provided for developers to port existing apps written for other platforms (Windows Win32, Unix, etc) to OS X. It's an alright API but it's very similar to Win32 API programming on Windows, something you want to stay away from if you're just learning to program and want to remain sane. Look at my picture. I cut my hair off because I kept pulling it when I was programming on Windows
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Stick with C. Objective-C is the main language on OS X and it's very heavily dependent on C. If you don't know C, Objective-C will be completely alien to you and you'll have a very hard time.
C++ is a nice language, but unless you feel the need to prove your 'macho'ness, stay away from it. C++ is a complex beast of a language where most programmers only use a subset of features, and those who do make use of the advanced language features are notorious for writing code that is unreadable by the general programmer populace. While I've used C++ for nearly 6 years, I can't recommend this language unless there is an esoteric need that other languages like Java/C#/Objective-C can't meet.
One more thing before I forget, when starting out it's very tempting to do many languages/APIs at once. You might be able to cope, but you're more likely to burn out and give up in frustration. I suggest sticking to learning *one* language (in this case C), taking it easy and spending a few months (2 - 3 at least) getting to know the language, writing some simple text based apps before moving on. Doing this will allow you to become familiar with the language, the development tools, and programming in general. Once you're confident, you can move on to other languages or doing other things like GUI programming.