Beyond that, even, you can write Objective-C in pure C99. The brackets, class definitions, and all the rest is a sort of syntactic sugar that converts directly to a handful of straight C functions (you can find them all here: https://developer.apple.com/library/mac/#documentation/Cocoa...)
Not quite; Objective-C is a superset of C. You can write pure C and compile it as Objective-C all day long.
This is an important point because people think their C knowledge doesn't translate to Objective-C, mainly because people say things like "it's entirely different". At its core, it really isn't -- the superset syntax becomes straight C underneath.