August 1997
OP216: OBJECT ORIENTED PROGRAMMING

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

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Solutions and allocated marks are indicated in green.
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1. (a) What is the difference between public and private data members? [4]
Public members are accessed by the clients/friends of the class. They can be accessed at any time from outside the object. [2]
Private data members can only be accessed by member functions of the data. They are not intended to be invoked from outside an object. [2]
[4 marks]
(b) Use C++ to describe the header of a function called MEOW. MEOW is a member of the class cat but is defined outside it. MEOW takes no parameters and returns void. [2]
void Cat : : MEOW( );
deduct one mark for each syntax error or omission, minimum zero.
[2 marks]
(c) Use C++ to show the declaration of a class square that derives from rectangle, which in turn derives from shape [3]
class Square : Public Rectangle { };
deduct one mark for each syntax error or omission, minimum zero.
[3 marks]
(d) When is copy constructor called and when is a destructor called? [4]
A constructor is called whenever a temporary copy of an object is created. This happens everytime an object is passed by value. [2]
The destructor is called each time an object is destroyed, either because it goes out of scope or because a delete is applied to its pointer. [2]
[4 marks]
(e) Differentiate between the following:
(i) class and object [2]
A class is an implementation of an abstract data type while an object is an instance of a class. [2]
(ii) method and message [2]
A Message is a request to an object to invoke one of its methods. A Method is associated to a class and is invoked by a message. [2]
[4 marks]
(f) List the three types of inheritance. [3]
Public, Protected and Private Inheritance.
[3 marks]