Chapter 13

Question 1

1. What is the difference between a class and an instance of the class?

Answer 1

1. A class describes a data type. An instance of a class is an object of the data type that exists in memory.

Question 2

. What is the difference between the following Person structure and Person class?
struct Person
{
string name;
int age;
};
class Person
{
string name;
int age;
};

Answer 2

2. All members of a struct are public by default. The members of a class, however, are private by default.

Question 3

3. What is the default access specification of class members?

Answer 3

private

Question 4

4. Look at the following function header for a member function.
   void Circle::getRadius()
   What is the name of the function?
   What class is the function a member of?

Answer 4

4. The function’s name is getRadius. It is a member of the Circle class.

Question 5

5. A contractor uses a blueprint to build a set of identical houses. Are classes analogous to the blueprint or the houses?

Answer 5

5. A class is analogous to the blueprint.

Question 6

6. What is a mutator function? What is an accessor function?

Answer 6

6. A mutator is a member function that stores a value in a private member variable, or in some way changes an attribute. An accessor is a member function that retrieves the value stored in a private member variable.

Question 7

7. Is it a good idea to make member variables private? Why or why not?

Answer 7

7. Yes it is. This protects the variables from being directly manipulated by code outside the class, and prevents them from receiving invalid data.

Question 8

8. Can you think of a good reason to avoid writing statements in a class member function that use cout or cin ?

Answer 8

8. Unless a class is specifically designed to perform I/O, operations like user input and output are best left to the person designing the application. Classes should provide member functions for retrieving any important data without displaying them on the screen. Likewise, they should provide member functions that store data into private member variables without using cin. This allows a programmer to use the class without being locked into a particular method of performing I/O.

Question 9

9. Under what circumstances should a member function be private?

Answer 9

9. When the function is necessary for internal processing, but not useful to the program outside the class. In some cases a class may contain member functions that initialize member variables or destroy their contents. Those functions should not be accessible by an external part of program because they may be called at the wrong time.

Question 10

10. What is a constructor? What is a destructor?

Answer 10

10. A constructor is a member function that is automatically called when a class object is created. A destructor is a member function that is automatically called when a class object is destroyed.

Question 11

11. What is a default constructor? Is it possible to have more than one default constructor?

Answer 11

11. A default constructor is a constructor that is called without any arguments. It is not possible to have more than one default constructor.

Question 12

12. Is it possible to have more than one constructor? Is it possible to have more than one destructor?

Answer 12

12. Yes, it is possible to have more than one constructor. It is not possible to have more than one destructor.

Question 13

13. If a class object is dynamically allocated in memory, does its constructor execute? If so, when?

Answer 13

13. Yes, the constructor executes when the object is created.

Question 14

14. When defining an array of class objects, how do you pass arguments to the constructor for each object in the array?

Answer 14

14. You specify the arguments for each object individually in an initialization list.

Question 15

15. What are a class’s responsibilities?

Answer 15

15. A class’s responsibilities are the things that the class is responsible for knowing and the actions that the class is responsible for doing.

Question 16

16. How do you identify the classes in a problem domain description?

Answer 16

16. Identify all the nouns (including pronouns and noun phrases) in the problem domain description. Each of these is a potential class. Then, refine the list to include only the classes that are relevant to the problem.

Question 17

17. The two common programming methods in practice today are _________ and
    _________.

Answer 17

17. procedural programming, object-oriented programming

Question 18

18. ________ programming is centered around functions or procedures.

Answer 18

procedural

Question 19

19. ________ programming is centered around objects.

Answer 19

19. object-oriented

Question 20

20. ________ is an object’s ability to contain and manipulate its own data.

Answer 20

encapsulation

Question 21

21. In C++ the _________ is the construct primarily used to create objects.

Answer 21

class

Question 22

22. A class is very similar to a(n) _________.

Answer 22

structure

Question 23

23. A(n) _________ is a key word inside a class declaration that establishes a member’s accessibility.

Answer 23

23. access specifier

Question 24

24. The default access specification of class members is _________.

Answer 24

private

Question 25

26. Defining a class object is often called the _________ of a class.

Answer 25

instantiation

Question 26

25. The default access specification of a struct in C++ is _________.

Answer 26

public

Question 27

27. Members of a class object may be accessed through a pointer to the object by using the _________ operator.

Answer 27

27. ->

Question 28

28. If you were writing the declaration of a class named Canine , what would you name the file it was stored in? _________

Answer 28

canine.h

Question 29

29. If you were writing the external definitions of the Canine class’s member functions, you would save them in a file named _________.

Answer 29

29. canine.cpp

Question 30

30. When a member function’s body is written inside a class declaration, the function is

Answer 30

inline

Question 31

31. A(n) _________ is automatically called when an object is created.

Answer 31

constructor

Question 32

32. A(n) _________ is a member function with the same name as the class.

Answer 32

constructor

Question 33

33. ________ are useful for performing initialization or setup routines in a class object.

Answer 33

constructors

Question 34

34. Constructors cannot have a(n) _________ type.

Answer 34

return

Question 35

35. A(n) _________ constructor is one that requires no arguments.

Answer 35

default

Question 36

36. A(n) _________ is a member function that is automatically called when an object is destroyed.

Answer 36

destructor

Question 37

37. A destructor has the same name as the class, but is preceded by a(n) _________ character.

Answer 37

~

Question 38

38. Like constructors, destructors cannot have a(n) _________ type.

Answer 38

return

Question 39

39. A constructor whose arguments all have default values is a(n) _________ constructor.

Answer 39

default

Question 40

40. A class may have more than one constructor, as long as each has a different _________.

Answer 40

parameter list

Question 41

41. A class may only have one default _________ and one _________.

Answer 41

41. constructor, destructor

Question 42

42. A(n) _________ may be used to pass arguments to the constructors of elements in an object array.

Answer 42

42. initialization list

Question 43

51. T F Private members must be declared before public members.

Answer 43

false

Question 44

52. T F Class members are private by default.

Answer 44

true

Question 45

53. T F Members of a struct are private by default.

Answer 45

false

Question 46

54. T F Classes and structures in C++ are very similar.

Answer 46

true

Question 47

55. T F All private members of a class must be declared together.

Answer 47

false

Question 48

56. T F All public members of a class must be declared together.

Answer 48

false

Question 49

57. T F It is legal to define a pointer to a class object.

Answer 49

true

Question 50

58. T F You can use the new operator to dynamically allocate an instance of a class.

Answer 50

true

Question 51

59. T F A private member function may be called from a statement outside the class, as long as the statement is in the same program as the class declaration.

Answer 51

false

Question 52

60. T F Constructors do not have to have the same name as the class.

Answer 52

false

Question 53

61. T F Constructors may not have a return type.

Answer 53

true

Question 54

62. T F Constructors cannot take arguments.

Answer 54

false

Question 55

63. T F Destructors cannot take arguments.

Answer 55

true

Question 56

64. T F Destructors may return a value.

Answer 56

64. false

Question 57

65. T F Constructors may have default arguments.

Answer 57

true

Question 58

66. T F Member functions may be overloaded.

Answer 58

true

Question 59

67. T F Constructors may not be overloaded.

Answer 59

false

Question 60

68. T F A class may not have a constructor with no parameter list, and a constructor whose arguments all have default values.

Answer 60

true

Question 61

69. T F A class may only have one destructor.

Answer 61

true

Question 62

70. T F When an array of objects is defined, the constructor is only called for the first element.

Answer 62

false

Question 63

71. T F To find the classes needed for an object-oriented application, you identify all of the verbs in a description of the problem domain.

Answer 63

false

Question 64

72. T F A class’s responsibilities are the things the class is responsible for knowing, and actions the class must perform.

Answer 64

true

Question 65

73. class Circle:
    {
    private
    double centerX;
    double centerY;
    double radius;
    public
    setCenter(double, double);
    setRadius(double);
    }

Find the Errors

Answer 65

There should not be a colon after the word Circle.
Colons should appear after the words private and public.
A semicolon should appear after the closing brace.

Question 66

74. # include <iostream></iostream>using namespace std;
    Class Moon;
    {
    Private;
    double earthWeight;
    double moonWeight;
    Public;
    moonWeight(double ew);
    { earthWeight = ew; moonWeight = earthWeight / 6; }
    double getMoonWeight();
    { return moonWeight; }
    }
    int main()
    {
    double earth;
    cout&raquo_space; “What is your weight? “;
    cin &laquo_space;earth;
    Moon lunar(earth);
    cout &laquo_space;“On the moon you would weigh “
    «lunar.getMoonWeight() &laquo_space;endl;
    return 0;
    }

Find the Errors

Answer 66

The semicolon should not appear after the word Moon.
The first character of the words private and public should not be capitalized.
There should be a colon, not a semicolon, following the words private and public.
Semicolons should not appear in the member function headers.
In function main an argument is passed to a constructor that does not exist in the
Moon class.
The moonWeight member function should have been called prior to getMoonWeight.

Question 67

75. # include <iostream></iostream>using namespace std;
    class DumbBell;
    {
    int weight;
    public:
    void setWeight(int);
    };
    void setWeight(int w)
    {
    weight = w;
    }
    int main()
    {
    DumbBell bar;
    DumbBell(200);
    cout &laquo_space;“The weight is “ &laquo_space;bar.weight &laquo_space;endl;
    return 0;
    }

Find the Errors

Answer 67

The semicolon should not appear after the word DumbBell.
The function header for setWeight should appear as:
void DumbBell::setWeight(int w)
The line that reads:
DumbBell(200);
should read:
bar.setWeight(200);

bar.weight cannot be accessed outside of the class because no access specifier appeared before it in the class, making the variable private to the class by default. This means the cout statement will not work.

Question 68

76. class Change
    {
    public:
    int pennies;
    int nickels;
    int dimes;
    int quarters;
    Change()
    { pennies = nickels = dimes = quarters = 0; }
    Change(int p = 100, int n = 50, d = 50, q = 25);
    };
    void Change::Change(int p, int n, d, q)
    {
    pennies = p;
    nickels = n;
    dimes = d;
    quarters = q;
    }

Find the Errors

Answer 68

76. Both constructors are considered the default constructor.