What if one forget the  when deleteing array allocated through new T[n]?
A: All life comes to a disastrous end.
It is the programmer's responsibility not the compiler's to get the connection among new T[n] and delete p correct. If you get it incorrect, neither a compile-time nor a run-time error message will be generated through the compiler. Heap corruption is a likely result. Or worse. Your program will die probably.