The OS4, MOS & AROS definately need more programmers to work on apps so it's good to see that there is some interest.
Anybody learning to program should forget C, and focus on C++ instead. Some of the comments have suggested the opposite, because C++ is more complex. This is true, but the complicated language features aren't going to be even remotely touched upon by a beginner anyway.
The C++ features that a beginner will learn, such as I/O and the string class, are far simpler than C's equivalents anyway, and C, for the most part, is compilable in a C compiler.
As to the people who suggested learning Java - how is that going to benefit Amiga-ish systems?! If you know C++ you can learn any other language in no time, as it's the big beast of programming languages, but it wouldn't be the case with Java which is far simpler.