If you need a recursive search, you have a variety of options. You should consider ack.
Failing that, if you have GNU find and xargs:
find . -name '*.cc' -print0 -o -name '*.h' -print0 | xargs -0 grep hello /dev/null
The use of /dev/null ensures you get file names printed; the -print0 and -0 deals with file names containing spaces (newlines, etc).
If you don't have obstreperous names (with spaces etc), you can use:
find . -name '*.*[ch]' -print | xargs grep hello /dev/null
This might pick up a few names you didn't intend, because the pattern match is fuzzier (but simpler), but otherwise works. And it works with non-GNU versions of find and xargs.