Yves Papegay has developed SymbolicC in order to automate the conversion of his models to C. This is used by Airbus. 

For more information see his presentations in the Wolfram Library Archive http://library.wolfram.com/infocenter/search/?search_results=1&search_person_id=6281
especially this one http://library.wolfram.com/infocenter/Conferences/7477/

It can give ideas, but there are still many gaps to fill !

Also take a look at the installation folders Mathematica\8.0\AddOns\Applications\CCodeGenerator and Mathematica\8.0\AddOns\Applications\SymbolicC for examples.

**Edit**: I think that using SymbolicC under the hood with Compile and Mathematica code combined with my answer to http://mathematica.stackexchange.com/q/24595/66 you can compile a lot of things to C without explicitely using the SymbolicC package.