What are the different ways of combining C++ and C#?

Question

Possible Duplicate:
Writing a DLL in C/C++ for .Net interoperability

I am writing a school project in C++, where I would like to have a GUI written in C# with WPF.

This leads me to my question:

What are the different ways of combining unmanaged C++ and C# and what are the advantages of each?

Preferably I would like to have standard C++ code in a separate project, which I will then wrap (if needed), so I can build the C++ with a shell interface on Linux.

I am using VS2010 Ultimate.

Note: Writing the code in C# is not relevant. There are some details in the algorithm which make STL more suited than the equivalent classes on .NET. I would also like unmanaged code, so I can test the performance without GC pauses.