Im not sure why you consider working on coding, if you dont know what the errors are telling you. This regards coding basics, I'd advice you to stop here, and start with Hello-World Scripts to understand what you're actually doing. Cuz you dont seem to know lol.
For the quesiton itself: i and fX must be declared, for example like int i = 0;
Since im not familar with the flyff source, it'll be declared either in the function where ur code is itself, or in th 2DRender.h (if existant). But the cpp file makes more sense to me.
Good luck.
Edit/Note: Im more familar to C# coding, but the explaination should fit c++ just fine too. Also dont get my first comment wrong tho, it's not ment bad. Knowing the Basics will help you further investigate problems on your own, even tho I personally dont mind if people seek for help. I do that once in a while too i guess. Who's not hu? p: