December 1998 OP216: Object Oriented Programming (Question 1)

(a)	State, and briefly describe, the final stage of the Booch design methodolgy	[2]
	Implementation or reiterate the design (1 mark). Example descriptions: Reiterating the design can help solve problems with the program (1 mark); or help to fine tune earlier decisions (1 mark). Award (1 mark) for any suitable description.
(b)	In C++, a virtual function permits dynamic binding. Explain what is meant by dynamic binding and how it differs from static binding.	[2]
	Dynamic binding is the association of a name to a function at run-time (1 mark). Static binding associates names to functions at compile-time (1 mark).
(c)	Explain the use of the this pointer in C++.	[2]
	The this pointer is an implicit first argument to a method (1 mark) that is used to properly access the members of an object (1 mark).
(d)	Explain the difference between deep and shallow (or memberwise) copying of objects in C++.	[3]
	A shallow copy is used as the default to copy objects passed by value to a function (1 mark) where pointers in both copies to the same memory location (1 mark). A deep copy copies the data pointed to by a pointer to newly allocated memory (1 mark). Alternatively, (1 mark) for the correct reproduction of the diagram from the study guide, if it demonstrates a full understanding.
(e)	For either Java or Smalltalk, list two language features that are different from those found in C++.	[2]
	For Java, any two of: less complicated syntax (1 mark); run-time security mechanism (1 mark); support for multi-threading (1 mark). For Smalltalk, any two of: a pure object-oriented programming language (1 mark); uses late binding (1 mark); ease of development environment (1 mark). Award 1 mark for any alternative correct language feature.
(f)	(i) Explain the difference between passing arguments to a function by value and by reference.	[2]
	In call by value, the function receives a copy of the data item (1 mark). In call by reference, the function receives a pointer (or reference) to the actual data item (1 mark).
	(ii) Write a function that takes an array of integers and its integer length, and reverses the order of the integers in the array.	[7]
	int reverse(int a[], int n) {	[1]
	for (int i = 0; i < (n/2); i++) {	[2]
	int m;	[1]
	m = a[i];	[1]
	a[i] = a[n-i-1];	[1]
	a[n-i-1] = m;	[1]
	}
	} (1 mark) for a correct signature; (1 mark) for using the loop and (1 mark) for correct guard; (1 mark) for local variable; (1 mark) for assigning either the first or last item to local variable; (1 mark) for each correct swap. Do not penalise repeated errors.