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10Classes:

A Deeper Look,Part 2

O B J E C T I V E SIn this chapter you will learn:

■ To specify const (constant) objects and const member functions.

■ To create objects composed of other objects.

■ To use friend functions and friend classes.

■ To use the this pointer.

■

To create and destroy objects dynamically with operatorsnew and delete, respectively.

■ To use static data members and member functions.

■ The concept of a container class.

■ The notion of iterator classes that walk through theelements of container classes.

■ To use proxy classes to hide implementation details froma class’s clients.

But what, to serve our private ends,Forbids the cheating of our

friends?

—Charles Churchill

Instead of this absurddivision into sexes they oughtto class people as static anddynamic.

—Evelyn Waugh

Have no friends not equal to yourself.

—Confucius

2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currentlyNo portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.

For the exclusive use of adopters of the book C++ How to Program, 5th Edition,

by Deitel and Deitel. ISBN 0-13-185757-6.

Copyright ® 1992-2005 by Deitel & Associates, Inc. All Rights Reserved.



524 Chapter 10 Classes: A Deeper Look, Part 2

Self-Review Exercises

10.1 Fill in the blanks in each of the following:a) must be used to initialize constant members of a class. ANS : member initializers.b) A nonmember function must be declared as a(n) of a class to have access

to that class’s private data members. ANS : friend.c) The operator dynamically allocates memory for an object of a specified

type and returns a to that type. ANS : new, pointer.d) A constant object must be ; it cannot be modified after it is created. ANS : initialized.e) A(n) data member represents class-wide information. ANS : static.f) An object’s non-static member functions have access to a “self pointer” to the object

called the pointer.

ANS : this.g) The keyword specifies that an object or variable is not modifiable after it

is initialized. ANS : const.h) If a member initializer is not provided for a member object of a class, the object's

is called. ANS : default constructor.i) A member function should be declared static if it does not access class

members. ANS : non-static. j) Member objects are constructed their enclosing class object. ANS :

before.k) The operator reclaims memory previously allocated by new. ANS : delete.

10.2 Find the errors in the following class and explain how to correct them:

class Example {

public: Example( int y = 10 ) : data( y )

{

// empty body

} // end Example constructor

int getIncrementedData() const {

return data++;} // end function getIncrementedData

static int getCount() {

cout << "Data is " << data << endl;

return count; } // end function getCount

private: int data;




Exercises 525

static int count;}; // end class Example

ANS : Error: The class definition for Example has two errors. The first occurs in functiongetIncrementedData. The function is declared const, but it modifies the object.Correction: To correct the first error, remove the const keyword from the definitionof getIncrementedData.Error: The second error occurs in function getCount. This function is declaredstatic, so it is not allowed to access any non-static member of the class.Correction: To correct the second error, remove the output line from the getCount def-inition.

Exercises

10.3 Compare and contrast dynamic memory allocation and deallocation operators new, new [],delete and delete [].

ANS : Operator new creates an object and dynamically allocates space in memory for that

object. Operatordelete

destroys a dynamically allocated object and frees the spacethat was occupied by the object. Operators new [] and delete [] are used to allocateand deallocate arrays dynamically.

10.4 Explain the notion of friendship in C++. Explain the negative aspects of friendship as de-scribed in the text.

ANS : Functions that are declared as friends of a class have access to that class’s private

and protected members. Some people in the object-oriented programming commu-nity prefer not to use friend functions. Such people believe friendship corrupts in-formation hiding and weakens the value of the object-oriented design approach,because friend functions can directly access a class’s implementation details that aresupposed to be hidden.

10.5 Can a correct Time class definition include both of the following constructors? If not, ex-plain why not.

Time( int h = 0, int m = 0, int s = 0 );

Time();

ANS : No. There is ambiguity between the two constructors. When a call is made to the de-fault constructor, the compiler cannot determine which one to use because both con-structors can be called with no arguments.

10.6 What happens when a return type, even void, is specified for a constructor or destructor? ANS : A compilation error occurs. A programmer cannot specify a return type for a con-

structor or destructor.

10.7 Modify class Date in Fig. 10.10 to have the following capabilities:a) Output the date in multiple formats such as

DDD YYYY

MM/DD/YY

June 14, 1992

b) Use overloaded constructors to create Date objects initialized with dates of the formatsin part (a).





c) Create a Date constructor that reads the system date using the standard library functionsof the <ctime> header and sets the Date members. (See your compiler’s reference docu-mentation or www.cplusplus.com/ref/ctime/index.html for information on the func-tions in header <ctime>.)

In Chapter 11, we will be able to create operators for testing the equality of two dates and for com-

paring dates to determine whether one date is prior to, or after, another. ANS :

1 // Exercise 10.7 Solution: Date.h

2 // Date class definition; Member functions defined in Date.cpp

3 #ifndef DATE_H

4 #define DATE_H

5

6 #include <string>

7 using std::string;

8

9 class Date

10 {

11 public:

12 Date(); // default constructor uses <ctime> functions to set date

13 Date( int, int ); // constructor using ddd yyyy format

14 Date( int, int, int ); // constructor using dd/mm/yy format

15 Date( string, int, int ); // constructor using Month dd, yyyy format

16 void setDay( int ); // set the day

17 void setMonth( int ); // set the month

18 void print() const; // print date in month/day/year format

19 void printDDDYYYY() const; // print date in ddd yyyy format

20 void printMMDDYY() const; // print date in mm/dd/yy format

21 void printMonthDDYYYY() const; // print date in Month dd, yyyy format

22 ~Date(); // provided to confirm destruction order23 private:

24 int month; // 1-12 (January-December)

25 int day; // 1-31 based on month

26 int year; // any year

27

28 // utility functions

29 int checkDay( int ) const; // check if day is proper for month and year

30 int daysInMonth( int ) const; // returns number of days in given month

31 bool isLeapYear() const; // indicates whether date is in a leap year

32 int convertDDToDDD() const; // get 3-digit day based on month and day

33 void setMMDDFromDDD( int ); // set month and day based on 3-digit day

34 string convertMMToMonth( int ) const; // convert mm to month name

35 void setMMFromMonth( string ); // convert month name to mm36 int convertYYYYToYY() const; // get 2-digit year based on 4-digit year

37 void setYYYYFromYY( int ); // set year based on 2-digit year

38 }; // end class Date

39

40 #endif

1 // Exercise 10.7 Solution: Date.cpp

2 // Member-function definitions for class Date.

3 #include <iostream>




Exercises 527

4 using std::cout;

5 using std::endl;

6

7 #include <iomanip>

8 using std::setw;

9 using std::setfill;

10

11 #include <ctime>

12 using std::time;

13 using std::localtime;

14 using std::tm;

15 using std::time_t;

16

17 #include "Date.h" // include Date class definition

18

19 // default constructor that sets date using <ctime> functions

20 Date::Date()

21 {

22 // pointer of type struct tm which holds calendar time components23 struct tm *ptr;

24

25 time_t t = time( 0 ); // determine current calendar time

26

27 // convert current calendar time pointed to by t into

28 // broken down time and assign it to ptr

29 ptr = localtime( &t );30

31 day = ptr->tm_mday; // broken down day of month

32 month = 1 + ptr->tm_mon; // broken down month since January

33 year = ptr->tm_year + 1900; // broken down year since 1900

34 } // end Date constructor

35

36 // constructor that takes date in ddd yyyy format

37 Date::Date( int ddd, int yyyy )

38 {

39 year = yyyy; // could validate

40 setMMDDFromDDD( ddd ); // set month and day based on ddd


42

43 // constructor that takes date in mm/dd/yy format

44 Date::Date( int mm, int dd, int yy )

45 {

46 setYYYYFromYY( yy ); // set 4-digit year based on yy

47 setMonth( mm ); // validate and set the month48 setDay( dd ); // validate and set the day


50

51 // constructor that takes date in Month dd, yyyy format

52 Date::Date( string monthName, int dd, int yyyy )

53 {

54 setMMFromMonth( monthName ); // set month based on month name

55 setDay( dd ); // validate and set the day

56 year = yyyy; // could validate


58





59 // validate and store the day

60 void Date::setDay( int d )

61 {

62 day = checkDay( d ); // validate the day

63 } // end function setDay

64

65 // validate and store the month66 void Date::setMonth( int m )

67 {

68 if ( m > 0 && m <= 12 ) // validate the month

69 month = m;

70 else

71 {72 month = 1; // invalid month set to 1

73 cout << "Invalid month (" << m << ") set to 1.\n";

74 } // end else

75 } // end function setMonth

76

77 // print Date object in form: month/day/year78 void Date::print() const

79 {

80 cout << month << '/' << day << '/' << year << endl;

81 } // end function print

82

83 // print Date object in form: ddd yyyy

84 void Date::printDDDYYYY() const85 {

86 cout << convertDDToDDD() << ' ' << year << endl;

87 } // end function printDDDYYYY

88

89 // print Date object in form: mm/dd/yy

90 void Date::printMMDDYY() const91 {

92 cout << setw( 2 ) << setfill( '0' ) << month << '/'

93 << setw( 2 ) << setfill( '0' ) << day << '/'

94 << setw( 2 ) << setfill( '0' ) << convertYYYYToYY() << endl;

95 } // end function printMMDDYY

96

97 // print Date object in form: Month dd, yyyy

98 void Date::printMonthDDYYYY() const

99 {

100 cout << convertMMToMonth( month ) << ' ' << day << ", " << year

101 << endl;

102} // end function printMonthDDYYYY103

104 // output Date object to show when its destructor is called

105 Date::~Date()

106 {

107 cout << "Date object destructor for date ";

108 print();

109 cout << endl;

110 } // end ~Date destructor

111

112 // utility function to confirm proper day value based on

113 // month and year; handles leap years, too




Exercises 529

114 int Date::checkDay( int testDay ) const

115 {

116 // determine whether testDay is valid for specified month

117 if ( testDay > 0 && testDay <= daysInMonth( month ) )

118 return testDay;

119

120 // February 29 check for leap year121 if ( month == 2 && testDay == 29 && isLeapYear() )

122 return testDay;

123

124 cout << "Invalid day (" << testDay << ") set to 1.\n";

125 return 1; // leave object in consistent state if bad value

126 } // end function checkDay127

128 // return the number of days in a month

129 int Date::daysInMonth( int m ) const

130 {

131 if ( isLeapYear() && m == 2 )

132 return 29;133

134 static const int daysPerMonth[ 13 ] =

135 { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

136

137 return daysPerMonth[ m ];

138 } // end function daysInMonth

139

140 // test for a leap year

141 bool Date::isLeapYear() const

142 {

143 if ( year % 400 == 0 || ( year % 4 == 0 && year % 100 != 0 ) )

144 return true;

145 else146 return false;

147 } // end function isLeapYear

148

149 // calculate 3-digit day based on Date object's current month and day

150 int Date::convertDDToDDD() const

151 {

152 int ddd = 0;

153

154 // for each month that has passed, add days to ddd

155 for ( int i = 1; i < month; i++ )

156 ddd += daysInMonth( i );

157 158 // add days from current month

159 ddd += day;

160

161 return ddd;

162 } // end function convertDDToDDD

163

164 // set month and day based on 3-digit day

165 void Date::setMMDDFromDDD( int ddd )

166 {

167 int dayTotal = 0;

168 int m;





169

170 for ( m = 1; m <= 12 && ( dayTotal + daysInMonth( m ) ) < ddd; m++ )

171 dayTotal += daysInMonth( m );

172

173 setMonth( m );

174 setDay( ddd - dayTotal );

175 } // end function setMMDDFromDDD176

177 // utility function to convert month number to month name

178 string Date::convertMMToMonth( int mm ) const

179 {

180 static const string months[] =

181 { "", "January", "February", "March", "April", "May", "June",182 "July", "August", "September", "October", "November", "December" };

183

184 return months[ mm ];

185 } // end function convertMMToMonth

186

187 // set month number based on month name188 void Date::setMMFromMonth( string m )

189 {

190 bool matchFound = false;

191

192 // loop for each month, checking for a match

193 for ( int i = 1; i <= 12 && !matchFound; i++ )

194 {195 string tempMonth = convertMMToMonth( i );

196

197 if ( tempMonth == m )

198 {

199 setMonth( i );

200 matchFound = true;201 } // end if

202 } // end for

203

204 if ( !matchFound )

205 {

206 cout << "Invalid month name (" << month << "). month set to 1.\n";

207 setMonth( 1 ); // leave object in consistent state if bad value

208 } // end if

209 } // end function setMMFromMonth

210

211 // utility function to convert 4-digit year to 2-digit year

212int Date::convertYYYYToYY() const213 {

214 // if year is in 2000s, subtract 2000

215 // else, assume year is in the 1900s and subtract 1900

216 return ( year >= 2000 ? year - 2000 : year - 1900 );

217 } // end function convertYYYYtoYY

218

219 // utility function to convert 2-digit year to 4-digit year

220 void Date::setYYYYFromYY( int yy )

221 {

222 // if yy is less than 7, assume its in the 2000s

223 // if yy is greater than or equal to 7, assume it's in the 1900s




Exercises 531

224 year = ( yy < 7 ? yy + 2000 : yy + 1900 );

225 } // end function setYYYYFromYY

1 // Exercise 10.7 Solution: ex10_07.cpp

2 // Driver program for class Date.3 #include <iostream>

4 using std::cout;

5 using std::endl;

6

7 #include "Date.h" // include Date class definition

8

9 int main()

10 {

11 Date date1( 256, 1999 ); // initialize using ddd yyyy format12 Date date2( 3, 25, 04 ); // initialize using mm/dd/yy format

13 Date date3( "September", 1, 2000 ); // "month" dd, yyyy format

14 Date date4; // initialize to current date with default constructor

1516 // print Date objects in default format

17 date1.print();

18 date2.print();

19 date3.print();

20 date4.print();

21 cout << '\n';

22

23 // print Date objects in 'ddd yyyy' format

24 date1.printDDDYYYY();



27 date4.printDDDYYYY();28 cout << '\n';

29

30 // print Date objects in 'mm/dd/yy' format

31 date1.printMMDDYY();




35 cout << '\n';

36

37 // print Date objects in '"month" d, yyyy' format

38 date1.printMonthDDYYYY();

39 date2.printMonthDDYYYY();

40 date3.printMonthDDYYYY();41 date4.printMonthDDYYYY();

42 cout << endl;

43

44 return 0;

45 } // end main





10.8 Create a SavingsAccount class. Use a static data member annualInterestRate to store theannual interest rate for each of the savers. Each member of the class contains a private data member

savingsBalance indicating the amount the saver currently has on deposit. Provide member func-tion calculateMonthlyInterest that calculates the monthly interest by multiplying the balance by annualInterestRate divided by 12; this interest should be added to savingsBalance. Provide a static member function modifyInterestRate that sets the static annualInterestRate to a new value. Write a driver program to test class SavingsAccount. Instantiate two different objects of classSavingsAccount, saver1 and saver2, with balances of $2000.00 and $3000.00, respectively. Set theannualInterestRate to 3 percent. Then calculate the monthly interest and print the new balancesfor each of the savers. Then set the annualInterestRate to 4 percent, calculate the next month’sinterest and print the new balances for each of the savers.

ANS :

9/13/19993/25/20049/1/200012/14/2004

256 199985 2004245 2000349 2004

09/13/9903/25/0409/01/0012/14/04

September 13, 1999March 25, 2004September 1, 2000

December 14, 2004

Date object destructor for date 12/14/2004




1 // SavingsAccount.h2 // Header file for class SavingsAccount.

3 #ifndef SAVINGS_ACCOUNT_H

4 #define SAVINGS_ACCOUNT_H

5

6 class SavingsAccount

7 {

8 public:

9 // constructor sets balance to value greater than or equal to zero

10 SavingsAccount( double b )

11 {

12 savingsBalance = ( b >= 0.0 ? b : 0.0 );




Exercises 533

13 } // end SavingsAccount constructor

14

15 void calculateMonthlyInterest(); // calculate interest; add to balance

16 static void modifyInterestRate( double );

17 void printBalance() const;

18 private:

19 double savingsBalance; // the account balance20 static double annualInterestRate; // the interest rate of all accounts

21 }; // end class SavingsAccount

22

23 #endif

1 // Exercise 10.8 Solution: SavingsAccount.cpp

2 // Member-function defintions for class SavingsAccount.3 #include <iostream>

4 using std::cout;

5 using std::fixed;


8 using std::setprecision;

9

10 #include "SavingsAccount.h" // SavingsAccount class definition

11

12 // initialize static data member

13 double SavingsAccount::annualInterestRate = 0.0;

14

15 // calculate monthly interest for this savings account

16 void SavingsAccount::calculateMonthlyInterest()

17 {

18 savingsBalance += savingsBalance * ( annualInterestRate / 12.0 );19 } // end function calculateMonthlyInterest

20

21 // function for modifying static member variable annualInterestRate

22 void SavingsAccount::modifyInterestRate( double i )

23 {

24 annualInterestRate = ( i >= 0.0 && i <= 1.0 ) ? i : 0.03;

25 } // end function modifyInterestRate

26

27 // prints balance of the savings account

28 void SavingsAccount::printBalance() const

29 {

30 cout << fixed << '$' << setprecision( 2 ) << savingsBalance;

31 } // end function printBalance


2 // Driver program for class SavingsAccount.


4 using std::cout;

5 using std::endl;

6


8 using std::setw;

9





10.9 Create class IntegerSet for which each object can hold integers in the range 0 through 100. A set is represented internally as an array of ones and zeros. Array element a[ i ] is 1 if integer i isin the set. Array element a[ j ] is 0 if integer j is not in the set. The default constructor initializesa set to the so-called “empty set,” i.e., a set whose array representation contains all zeros.

Provide member functions for the common set operations. For example, provide a unionOfSets

member function that creates a third set that is the set-theoretic union of two existing sets (i.e., anelement of the third set’s array is set to 1 if that element is 1 in either or both of the existing sets, andan element of the third set’s array is set to 0 if that element is 0 in each of the existing sets).

10 #include "SavingsAccount.h" // SavingsAccount class definition

11

12 int main()

13 {

14 SavingsAccount saver1( 2000.0 );

15 SavingsAccount saver2( 3000.0 );

16

17 SavingsAccount::modifyInterestRate( .03 ); // change interest rate

18

19 cout << "Initial balances:\nSaver 1: ";

20 saver1.printBalance();

21 cout << "\tSaver 2: ";

22 saver2.printBalance();23

24 saver1.calculateMonthlyInterest();


26

27 cout << "\n\nBalances after 1 month's interest applied at .03:\n"

28 << "Saver 1: ";29 saver1.printBalance();



32

33 SavingsAccount::modifyInterestRate( .04 ); // change interest rate


35 saver2.calculateMonthlyInterest();36

37 cout << "\n\nBalances after 1 month's interest applied at .04:\n"

38 << "Saver 1: ";



41 saver2.printBalance();42 cout << endl;

43 return 0;

44 } // end main

Initial balances:Saver 1: $2000.00 Saver 2: $3000.00

Balances after 1 month's interest applied at .03:Saver 1: $2005.00 Saver 2: $3007.50

Balances after 1 month's interest applied at .04:

Saver 1: $2011.68 Saver 2: $3017.53





1 // Exercise 10.9 Solution: IntegerSet.cpp

2 // Member-function definitions for class IntegerSet.


4 using std::cout;

5 using std::cin;

6 using std::cerr;7


9 using std::setw;

10

11 #include "IntegerSet.h" // IntegerSet class definition

12

13 // constructor creates a set from array of integers

14 IntegerSet::IntegerSet( int array[], int size)

15 {

16 emptySet();

17

18 for ( int i = 0; i < size; i++ )

19 insertElement( array[ i ] );

20 } // end IntegerSet constructor

21

22 // initializes a set to the empty set

23 void IntegerSet::emptySet()24 {

25 for ( int y = 0; y < 101; y++ )

26 set[ y ] = 0;

27 } // end function emptySet

28

29 // input a set from the user

30 void IntegerSet::inputSet()

31 {32 int number;

33

34 do

35 {

36 cout << "Enter an element (-1 to end): ";37 cin >> number;

38

39 if ( validEntry( number ) )

40 set[ number ] = 1;

41 else if ( number != -1 )

42 cerr << "Invalid Element\n";

43 } while ( number != -1 ); // end do...while

44

45 cout << "Entry complete\n";

46 } // end function inputSet

47

48 // prints the set to the output stream

49 void IntegerSet::printSet() const

50 {

51 int x = 1;

52 bool empty = true; // assume set is empty

53

54 cout << '{';

55





111 set[ m ] = 0;

112 else

113 cerr << "Invalid delete attempted!\n";

114 } // end function deleteElement

115

116 // determines if two sets are equal

117 bool IntegerSet::isEqualTo( const IntegerSet &r ) const118 {

119 for ( int v = 0; v < 101; v++ )

120 if ( set[ v ] != r.set[ v ] )

121 return false; // sets are not-equal

122

123 return true; // sets are equal124 } // end function isEqualTo


2 // Driver program for class IntegerSet.

3 #include <iostream>4 using std::cout;

5 using std::endl;

6

7 #include "IntegerSet.h" // IntegerSet class definition

8

9 int main()

10 {

11 IntegerSet a;

12 IntegerSet b;

13 IntegerSet c;

14 IntegerSet d;

15

16 cout << "Enter set A:\n";

17 a.inputSet();

18 cout << "\nEnter set B:\n";

19 b.inputSet();

20 c = a.unionOfSets( b );

21 d = a.intersectionOfSets( b );

22 cout << "\nUnion of A and B is:\n";

23 c.printSet();

24 cout << "Intersection of A and B is:\n";

25 d.printSet();

26

27 if ( a.isEqualTo( b ) )

28 cout << "Set A is equal to set B\n";29 else

30 cout << "Set A is not equal to set B\n";

31

32 cout << "\nInserting 77 into set A...\n";

33 a.insertElement( 77 );

34 cout << "Set A is now:\n";

35 a.printSet();

36

37 cout << "\nDeleting 77 from set A...\n";

38 a.deleteElement( 77 );

39 cout << "Set A is now:\n";




Exercises 539

10.10 It would be perfectly reasonable for the Time class of Figs. 10.18–10.19 to represent thetime internally as the number of seconds since midnight rather than the three integer values hour,minute and second. Clients could use the same public methods and get the same results. Modify

40 a.printSet();

41

42 const int arraySize = 10;

43 int intArray[ arraySize ] = { 25, 67, 2, 9, 99, 105, 45, -5, 100, 1 };

44 IntegerSet e( intArray, arraySize );

45

46 cout << "\nSet e is:\n";47 e.printSet();

48

49 cout << endl;

50

51 return 0;

52 } // end main

Enter set A:Enter an element (-1 to end): 45

Enter an element (-1 to end): 76


Enter an element (-1 to end): 6Enter an element (-1 to end): -1

Entry complete

Enter set B:Enter an element (-1 to end): 34




Enter an element (-1 to end): -1

Entry complete

Union of A and B is:

{ 6 8 34 45 76 93 }Intersection of A and B is:{ 34 45 }Set A is not equal to set B

Inserting 77 into set A...Set A is now:{ 6 34 45 76 77 }

Deleting 77 from set A...Set A is now:{ 6 34 45 76 }Invalid insert attempted!Invalid insert attempted!

Set e is:{ 1 2 9 25 45 67 99 100 }





the Time class of Fig. 10.18 to implement the time as the number of seconds since midnight andshow that there is no visible change in functionality to the clients of the class. [Note: This exercisenicely demonstrates the virtues of implementation hiding.]

ANS :

1 // Exercise 10.10 Solution: Time.h

2 // Time class definition; Member functions defined in Time.cpp.

3 #ifndef TIME_H

4 #define TIME_H

5

6 class Time

7 {

8 public:

9 Time( int = 0, int = 0, int = 0 ); // default constructor

10

11 // set functions (the Time & return types enable cascading)

12 Time &setTime( int, int, int ); // set hour, minute, second

13 Time &setHour( int ); // set hour14 Time &setMinute( int ); // set minute

15 Time &setSecond( int ); // set second

16

17 // get functions (normally declared const)

18 int getHour() const; // return hour

19 int getMinute() const; // return minute

20 int getSecond() const; // return second

21

22 // print functions (normally declared const)

23 void printUniversal() const; // print universal time

24 void printStandard() const; // print standard time

25 private:

26 int totalSeconds; // number of seconds since midnight27 }; // end class Time

28

29 #endif

1 // Exercise 10.10 Solution: Time.cpp

2 // Member-function definitions for Time class.


4 using std::cout;

5


7 using std::setfill;8 using std::setw;

9

10 #include "Time.h" // Time class definition

11

12 // constructor function to initialize private data;

13 // calls member function setTime to set variables;

14 // default values are 0 (see class definition)

15 Time::Time( int hr, int min, int sec )

16 {

17 setTime( hr, min, sec );

18 } // end Time constructor




Exercises 541

19

20 // set values of hour, minute, and second

21 Time &Time::setTime( int h, int m, int s ) // note Time & return

22 {

23 setHour( h );

24 setMinute( m );

25 setSecond( s );26 return *this; // enables cascading

27 } // end function setTime

28

29 // set hour value

30 Time &Time::setHour( int h ) // note Time & return

31 {32 int hours = ( h >= 0 && h < 24 ) ? h : 0;

33 totalSeconds = ( hours * 3600 ) + ( getMinute() * 60 ) + getSecond();

34 return *this; // enables cascading

35 } // end function setHour

36

37 // set minute value38 Time &Time::setMinute( int m ) // note Time & return

39 {

40 int minutes = ( m >= 0 && m < 60 ) ? m : 0;

41 totalSeconds = ( getHour() * 3600 ) + ( minutes * 60 ) + getSecond();

42 return *this; // enables cascading

43 } // end function setMinute

44

45 // set second value

46 Time &Time::setSecond( int s ) // note Time & return

47 {

48 int seconds = ( s >= 0 && s < 60 ) ? s : 0;

49 totalSeconds = ( getHour() * 3600 ) + ( getMinute() * 60 ) + seconds;

50 return *this; // enables cascading51 } // end function setSecond

52

53 // get hour value

54 int Time::getHour() const

55 {

56 return ( totalSeconds / 3600 );

57 } // end function getHour

58

59 // get minute value

60 int Time::getMinute() const

61 {

62 return ( ( totalSeconds % 3600 ) / 60 );63 } // end function getMinute

64

65 // get second value

66 int Time::getSecond() const

67 {

68 return ( ( totalSeconds % 3600 ) % 60 );

69 } // end function getSecond

70

71 // print Time in universal-time format (HH:MM:SS)

72 void Time::printUniversal() const

73 {





74 cout << setfill( '0' ) << setw( 2 ) << getHour() << ":"

75 << setw( 2 ) << getMinute() << ":" << setw( 2 ) << getSecond();

76 } // end function printUniversal

77

78 // print Time in standard-time format (HH:MM:SS AM or PM)

79 void Time::printStandard() const

80 {81 int hour = getHour();

82 cout << ( ( hour == 0 || hour == 12 ) ? 12 : hour % 12 )

83 << ":" << setfill( '0' ) << setw( 2 ) << getMinute()

84 << ":" << setw( 2 ) << getSecond() << ( hour < 12 ? " AM" : " PM" );

85 } // end function printStandard

1 // Exercise 10.10 Solution: ex10_10.cpp2 // Driver program for Time class.


4 using std::cout;

5 using std::endl;6

7 #include "Time.h" // Time class definition

8

9 int main()

10 {

11 Time t; // create Time object

12

13 // cascaded function calls

14 t.setHour( 18 ).setMinute( 30 ).setSecond( 22 );

15

16 // output time in universal and standard formats

17 cout << "Universal time: ";18 t.printUniversal();

19

20 cout << "\nStandard time: ";

21 t.printStandard();

22

23 cout << "\n\nNew standard time: ";

24

25 // cascaded function calls

26 t.setTime( 20, 20, 20 ).printStandard();

27 cout << endl;

28 return 0;

29 } // end main

Universal time: 18:30:22Standard time: 6:30:22 PM

New standard time: 8:20:20 PM

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