When amount of memory to be allocated is known beforehand i.e. at the the time of compilation, it is known as Static Memory Allocation. Once the memory is allocated statically, it cannot be deallocated during program run. So it leads to wastage of storage space.

Example:

int A[100];

When amount of memory to be allocated is not known beforehand, rather it is determined at the time of program run, it is called Dynamic Memory Allocation. It leads to efficient utilization of storage space.

Example:

cout << " Enter number of elements: ";

cin >> N;

int *A = new int[N]; // dynamic memory allocation

Polymorphism is also achieved in C++ using virtual functions. If a function with same name exists in base as well as parent class, then the pointer to the base class would call the functions associated only with the base class. However, if the function is made virtual and the base pointer is initialized with the address of the derived class, then the function in the child class would be called.

- Free() - A block of memory previously allocated by the malloc subroutine is freed by free subroutine. Undefined results come out if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will take place.

- Realloc() - This subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must be created with the malloc, calloc, or realloc subroutines and should not be deallocated with the free or realloc subroutines. Undefined results show up if the Pointer parameter is not a valid pointer.

Scope resolution operator allows a program to reference an identifier in the global scope that is hidden by another identifier with the same name in the local scope.

Stack unwinding is a process of calling all destructors for all automatic objects constructed at run time when an exception is thrown. Destructors are called between the places where the exception was thrown and where it is caught.

Wrapper classes wrap primitive values in a class and offers utility to access them through objects. Some of the primitive wrapper data types are:

Byte, short, int, long, float, double, char, Boolean.

Example: 

Create a class name VectorAdd to populate it with integer values using the add(int, object) method.

public class VectorAdd

{

       public static void main(String argv[])

       {

             Vector v = new Vector();

             v.add(0,new Integer(10));

             v.add(1,new Integer(20));

             v.add(2,new Integer(30));

             for(int i=0; i < v.size();i ++)

             {

                  Integer iw =(Integer) v.get(i);

                  System.out.println(iw);

             }

       }

}

A Stack is a linear structure in which insertions and deletions are always made at one end i.e the top - this is termed as last in, first out (LIFO). Stacks are useful when we need to check some syntex errors like missing parentheses. 

- Friend classes are useful when a class wants to hide features from users which are needed only by another, tightly coupled class. 

- Implementation details can be kept safe by providing friend status to a tightly cohesive class.