[pjmlp]

Only if they aren't using anything beyond C99, because after that C is basically turning into C++ without Classes.

[gingerBill]

Most C programmers I know pretty much do that. I use C11 just for the atomics and that is it. And I know many C programmers who still use C89/C90 exclusively.

[johnisgood]

Well yeah, I use C99. I would never use newer C, it is too C++-esque. You can actually use some stuff from stdatomic.h with -std=c99 -D_XOPEN_SOURCE=700, such as "atomic_bool" and whatnot.