Aztec C
on the Apple ][ is a sorry, lazy, flea-ridden dog.
Any C implementation for that
era (1979) of micros is a pretty good
find, IMHO.
Although I'd reccomend finding a C for the PC class, post
8086, (1985+) if what you want to learn is software.
A lot of 'free' 8086 C compilers are now out for the
with the demise of DOS.