Working with C Functions

I have a library of C functions that I have compiled into a DLL. I want to use these C functions from within my C# code. I have duplicated my C data structures in C# and I am able to marshal from C# to C. Is it possible to marshal an array of objects from C# to C, and if so how do I do it? The C library contains extremely complex calculations and it is not feasible to port and test given the project time constraints. Thanks Ross