i have been reading some books that they used/ include ADT in their class. in the ADT class there was many virtual function and some pure virtual function (with =0), this is the part i don't really understand, they use pure virtual function in ADT class. After they implement to other class, they function with same name as the virtual function which will override them, for other usage.. so what's the purpose of virtual function and pure virtual function? what's the purpose using ADT?
Pure virtual functions are used when a default implementation for the function isn't needed or wanted.
In that case the base class becomes an abstract type that cannot be instantiated as an object.
You are wrong. Pure virtual functions may have a default implementation.