0Converting a derived-class reference or pointer to a base-class reference or pointer is called upcasting. It is always allowed for public inheritance without the need for an explicit type cast.
The downcasting, the opposite of upcasting, is a process converting a base-class pointer or reference to a derived-class pointer or reference.
It is not allowed without an explicit type cast. That's because a derived class could add new data members, and the class member functions that used these data members wouldn't apply to the base class.
