As I understand correctly, besides the fact that Objective-C language is a strict superset of a \"clean\" C, added OOP paradigm is simulated by a set of functions partially
As far as I know, there is no software that preprocesses Objective-C code into intermediate C code.
But you could write your Objective-C program entirely in C by calling directly into the Objective-C runtime. The trouble is just that the code might vary between implementations or even different versions of the same runtime.
The question is, is it actually worth the trouble?
You could use the clang rewriter to convert to C++. Not aware of a way to go to C though.
The rewriter is available via the "-rewrite-objc" command line option.