How to call R from C function

He guys
It took me weeks to find a way to answer this question "How am I able to call R functions from C code?". You may start asking, why even do you need to intergrate these two ?
I would like to encourge you to read the paper I have uploaded (in the download section of my weblog) to find out why do I need and how you can get this job done.
Enjoy