how to complie .c and cuda? not .cpp

Hi Everyone

I am trying to integrate .C files (not C++) with CUDA, and I have seen the SDK example “cppintegration”
which use the extern “C”, but it doesn’t work for the .C files and shows

error C2059: syntax error : ‘string’

I learned that extern “C” only works for C++, but what if I want to complie .c files instead of .cpp?
Could anybody please help me out?

Thank you very much!