If you know C++, and already have working Windows code, then you shouldn't need a template. What you need to do is identify the parts of the program that aren't supported by Linux (the GUI code will probably need to be redone using some framework such as Qt or whatever - don't know C/C++ and Linux myself, Java's much easier!) and try Google to find tutorials or articles that tell you how to do 'em.
Maybe if you explain more about what the app must do, you'll get better responses than mine. Good luck.