You haven't given enough information. My guess is that you have declared your classes in different header files, with a dependency between them. For example, you might have Vehicle.h which declares Vehicle, Boat.h which declares Boat. If Boat.h or Car.h do not #include "Vehicle.h" that might explain your error message.
You also need to #include <iostream> before any usage of std::cout. That might also account for your error.
Unrelated to your problem, but both your derived classes have an int member named itsType. It may be appropriate, from a design perspective, for your base class to provide that member. Also, from a design perspective, it may be appropriate for your base class to provide some virtual methods that derived classes override, rather than having your derived classes introduce new characteristics.
And, lastly, NEVER NEVER NEVER use comments of the form
There are serious gotchas with that style of comment (eg if you hit a shift key at the wrong time while holding down a / key, you can introduce a digraph or trigraph and comment out following lines without realising it).