C++ is a great language to program with if you now how to do. Otherwise it gives you to many choices and it's likely you never get of the ground. Then better use C.
Now, C++ is backwards compatible with C and most programmers are actually only wrapping C into C++ containers to make it look like C++, which you could do ofcourse.
As for compilers for the Amiga there are a few I now of.
SAS C 6.5 - Dead, some C++ support with patches. But linking C++ object files appears not to work properly.
StormC 3.0 - Available on Amiga Developer CD 2.1. C++ supported, but lacks basic features like namespace. There is StormC 4.0 with PPC support that may be better, but I wouldn't count on it.
VBCC - *FREE* Don't support C++.
GCC - *FREE* Most advanced C/C++ compiler available. But, if your not a UNIX geek you will get gray hairs long before you compiled your first hello world example.
The best part with StormC is that it has an IDE which is good if you are a beginner.