Dec1999 OP216 : Object Oriented Programming (Question 5) Suggested Solutions

Consider the following abstract data type declaration for an IntegerList type:

class IntegerList {
private:
	int*s;
	int n;
public:
	IntegerList(int m,int*t);			//Copy n characters from t to s
	int Length(){return n;}			//Return the length of the list
	void UpdateAt(int i,int c)			{
		if(i>=0 &&i<=length())s [i ]=c;
	}		//Update the element at index i with element c
	int ElementAt(int i){
			if(i>=0 &&i<=length())return s [i ];else return 0;
	}		//Return the element at index i };
};

(a)

Explain the difference between deep and shallow (or member-wise) copying of objects.

•A shallow copy is the default copy for objects passed by value to a function;
(1 mark)
•Where both pointers point to the same memory location;(1 mark)
•A deep copy copies the data pointed to,to a newly allocated block of memory.
(1 mark)

[3]

(b)

Write a constructor function for the IntegerList class which performs a deep copy of the object.You may not use any library functions.

A sample definition of the constructor function IntegerList follows:

IntegerList::IntegerList(const IntegerList&p) {
	n=p.n; s=new int [n ]; for(int i=0;i<n;i++) s [i ]=p.s [i ];
}

And the following marking scheme should be used:
•A correct signature with const references;(1 mark)
•Assigning the length of the new object;(1 mark)
•Allocating space for the new IntegerList ;(1 mark)
•Declaring a suitable iterative structure;(1 mark)
•Bound by the source IntegerList length;(1 mark)
•Assigning the indexed element on each iteration.(1 mark)
[6 marks ]

[6]

(c)

Write a function Reverse ,the signature of which is given below,which takes an IntegerList object and returns a new IntegerList which is the reverse of the original IntegerList .You may not use any library functions.
IntegerList Reverse(IntegerList s);

A sample definition of Reverse follows:

IntegerList Reverse(IntegerList q) {
	IntegerList p=q; int i=0; int j=q.Length(); while(i<q.Length()){
		p.UpdateAt(j, q.ElementAt(i)); i++; j--; }
	return p;
}

And the following marking scheme should be used:
•Declaring a local IntegerList variable;(1 mark)
•Declaring and initialising local variables i and jj ;(1 mark)
•Declaring a suitable iterative structure;(1 mark)
•Bound by the IntegerList length conditions;(1 mark)
•Updating the indexed elements on each iteration;(1 mark)
•Returning the reversed IntegerList .(1 mark)
[6 marks ]

[6]