Main.cpp has no idea that the other 2 files exist, and the other 2 files have no idea that each other exist either.
You need to use the pre-processor directive #include to include the files where they are needed.
I would suggest reading some tutorials on the web, a search on google for "C++ Tutorial" will get you a wealth of info. The problem is one that you would know how to solve yourself(or more than likely just wouldnt have) if you spent a little time learning the language before jumping into it. It is complex in some aspects, but well worth taking the time to learn properly.
To use an analagy, with absolutely no offence intended, trying to use c++ without first learning the language basics(which it really doesnt take too long to do), is similar to jumping into a swimming pool's deep end, with no idea of how to swim, you may not drown, but you will have a really hard time staying afloat...
If it ain't broke.... DONT FIX IT !!!