Probably not. C doesn't exist in a vacuum: it has to run on something. And the standard library doesn't get you very far. You'd need to know at least one OS

Probably not. C doesn't exist in a vacuum: it has to run on something. And the standard library doesn't get you very far. You'd need to know at least one OS API as well: POSIX is probably best, maybe Win32, an embedded OS/executive might work also, or perhaps even a bare-metal CPU or two. C + POSIX covers a lot of the Open Source world, and increasingly more of the embedded market. C + VxWorks is possibly the next best combo.