December 1998 OP216: Object Oriented Programming (Question 4)

(a)	You are to design a C++ program for creating and manipulating entries in a telephone book. Consider the following class definition for a Person entry in a telephone book. class Person { public: char name; // the last name of the person in the book int number; // the telephone number of the person Person() {number = 0; name = 0;} // Constructor Person(char s, int n) { // Constructor number = n; name = s; } void display() { // Display a person cout << name << " has number " << number << endl; } };
(a)	The telephone book is an array of 10,000 Person entries and also an integer that records the number of entries in the telephone book. Give the definition of a class Telephone_book that contains: (1) the private data items listed above and (2) a default constructor that initialises the number of entries to 0.	[3]
	class Telephone_book {
	private:
	Person book[10000];	[1]
	int n;	[1]
	public:
	Telephone_book() { n = 0; } };	[1]
(b)	Give the implementation of a methof display that displays the details of every person in the telephone book.	[3]
	void display() {
	for (int i = 0; i < n; i++)	[2]
	book[i].display();	[1]
	}; (1 mark) for using a loop and (1 mark) for correct loop guard; (1 mark) for correctly displaying each entry.
(c)	Give the implementation of a method add_person that reads a last name and a telephone number from the user, creates a new person, and adds the person to the end of the array if there is a space.	[8]
	void add_person() {
	*char name = new char[50];**	[1]
	int m;	[1]
	cout << "Enter name: ";
	cin >> name;	[1]
	cout << "Enter number: ";
	cin >> m;	[1]
	if (entries < 10000) {	[1]
	Person e = Person(name, n);	[1]
	book[entries++] = e;	[2]
	} }; (1 mark) for each correct local variable declaration; (1 mark) for each correct input statement; (1 mark) for testing that there is space; (1 mark) for constructing the new Person; (1 mark) for assigning to book; (1 mark) for updating the number of entries.
(d)	Give the implementation of a method find that takes a telephone number and displays the person with the corresponding telephone number. If the telephone number does not exist in the telephone book, give an appropriate error message	[6]
	void find(int m) {
	for (int i=0; i < entries; i++)	[2]
	if (book[i].number == m) {	[1]
	book[i].display();	[1]
	return;	[1]
	}
	}
	cout << "Error: no such number" << endl;	[1]
	}; (2 marks) for correct use of a loop with increment and test; (1 mark) for checking numbers against m; (1 mark) for displaying the entry of the book; (1 mark) for terminating loop; (1 mark) for appropriate error message.