17.	Write the code for the push function in a vector implementation of a stack.  (The array might be full) 
refer to the source code of the text book

18.	Write the code for deleting an element in a queue. This is the deqeue() function. 
refer to the source code of the text book

19.	What is polymorphism? 

The ability of a reference variable to reference objects of several different types.
When operations are applied to the variable, the operation appropriate to object is automatically selected.

20.	Write a template class for finding minimum items in an array.


template <class Comparable>
const Comparable & min( const vector<Comparable> & array )
{
    int N = array.size( );
    int minItem = 0;
    for( int i = 1; i < n; i++ )
        if( array[ i ] < array[ minItem ] )
            minItem = i;
    return array[ minItem ];

}

21.	Please explain what happens in the stack (draw figures) of each step when the following program is run. 

see the figure in the slides of Chapter 8.

22.	Draw a picture of memory after these statements:
refer to the slides of Chapter 1.