CSC$240$ C$++$ classes and inheritance

Type in the following $C++$ program into a file classes.cpp$/$BASE CLASS$*****************************$class A$\{$protected:int x;public:A$()\{$ x $=0$;$\}$void increment$()\{$ x$++$; $\}$virtual void decrement$()\{$ x$--$; $\}\}$;void print$()\{$ cout x $="$ x $$ endl; $\}/$DERIVED CLASS$***********************/$class B : public A$|$public:void increment$()\{$ x $=$ x $+2$; $\}\}$;void decrement$()\{$ x $=$ x $-2$; $\}/$MAIN FUNCTION$*************************/$int main$()\{$A a; $//$ a is an object of class AA $*$ ptr; $//$ ptr is a pointer to an object of class Aptr $=$ &a;ptr $->$ increment$()$;ptr $->$ print$()$;ptr $->$ decrement$()$;ptr $->$ print$()$;$)$