Upcasting w/ Static Binding
When we use the statement member function with our
account pointer, the actual member function used is the
account's statement member function.
This is because static binding is in effect.
The member function bound by the compiler is based on
the static type of the pointer, not the actual or dynamic
type of the object pointed to.
Thus, even though the complete derived class object is
there, static binding prevents us from using the derived
class' statement member function.