CSCI 152 Quiz 5 ( 25/26 Apr )

Spring 2005 Name _______________________

1. Circle the following statements as true of false.

T F The data members of a class must be of the same type.

T F The function members of a class must be public.

T F A class can have more than one constructor.

T F The only built-in operations on classes are the assignment (=) and member access (.) operations.

T F A user-defined class can be used as the return type for a function.

T F A user-defined class can not be passed by reference as a parameter to a function.

T F Constructors are declared using the constructor keyword.

T F Constructors and destructors are functions without any return type.

T F Private members cannot be accessed by a user of the class.

T F A member of a class can be a function or a variable (that is data).

2. Given this C++ class specification:

class TelNum

{

public:

void PrintTelNum (); // prints to the screen like: 903-886-5409

void SetTelNum (int ac, int exch, int ext); // assigns parameter values

bool SameNum (TelNum otherNum); // returns true if two numbers are the same,

int GetAreaCode (); // returns area code

int GetExchange (); // returns exchange

int GetExtension (); // returns extension

private: // for 903-886-5409

int areaCode; // area code is 903

int exchange; // exchange is 886

int extension; // extension is 5409

};

a) Show how the client could declare class variables called myNum and yourNum to hold telephone numbers using the TelNum class.

TelNum myNum, yourNum;

b) Show how the client could assign the number 903-886-5409 to myNum.

myNum.SetTelNum(903, 886, 5409);

c) Show how the client could call the SameNum function and print YES if myNum is the

same as yourNum or print NO otherwise (assume both variables are assigned values).

if (myNum.SameNum(yourNum))

cout << “YES” << endl;

else

cout << “NO” << endl;

e) Show how the client could check to see if the area code of myNum is 903 (print YES if it

is or NO if it's not).

if (myNum.GetAreaCode() == 903)

cout << “YES” << endl;

else

cout << “NO” << endl;

f) Write the implementation (body) for the class function SetTelNum as it would appear in

the implementation file.

void TelNum::SetTelNum(int ac, int exch, int ext)

{

areaCode = ac;

exchange = exch;

extension = ext;

}

g) Assuming that the client has no other variables declared other than myNum and

yourNum, which of the following statements could the client code in a client program?

yes no 1) cout << myNum.areaCode;

yes no 2) yourNum = myNum;

yes no 3) if (myNum == yourNum) cout << “same number”;

yes no 4) int areaCode;

yes no 5) cout << myNum;

yes no 6) void DoSomething (TelNum & t); // client-defined function

yes no 7) TelNum DoSomethingElse (TelNum t); // client-defined function

yes no 8) extension = 5494;

h) What difference (if any) does it make to the client if the keyword "private:" is removed

from the class declaration (and everything else remains the same)?

The member variables (areaCode, exchange and extension) become public. This will mean that they can be directly changed by the client as they are no longer private. Will still work but might be dangerous, breaks encapsulation of the implementation of the TelNum class.

i) What difference (if any) does it make to the client if the keyword "public:" is removed

from the class declation (and everything else remains the same)?

Things are private by default in user defined classes. So without the “public” declaration, all of the member functions become private. This makes the class pretty useless as the client can no longer do anything with the class. All member functions and member variables are private so the client can no longer call them or access any of them.