2. Chapter 10
Defining Classes

3. Abstraction in Software Development
Abstraction allows a programmer to design a solution to a problem and to use data items without concern for how the data items are implemented
This has already been encountered in the book:
To use the pow function, you need to know what inputs it expects and what kind of results it produces
You do not need to know how it works

4. Abstraction and Data Types
Abstraction: a definition that captures general characteristics without details
ex: An abstract triangle is a 3-sided polygon. A specific triangle may be scalene, isosceles, or equilateral
Data Type: defines the kind of values that can be stored and the operations that can be performed on it

5. Abstraction and Data Types
Abstraction: a definition that captures general characteristics without details
ex: An abstract triangle is a 3-sided polygon. A specific triangle may be scalene, isosceles, or equilateral
Data Type: defines the kind of values that can be stored and the operations that can be performed on it

6. 7.1 Abstract Data Types
Structures/Classes that are defined by the operations that are performed by/on it.
Have no implementation shared
“interface contract” that the object provides

7. 7.1 Abstract Data Types Programmer-created data types that specify
legal values that can be stored
operations that can be done on the values
The user of an abstract data type (ADT) does not need to know any implementation details (e.g., how the data is stored or how the operations on it are carried out)

8. Overview
10.1 Structures ---- Object Oriented Programming 10.2 Classes 10.3 Abstract Data Types 10.4 Introduction to Inheritance

9. 10.1
Structures

10. Structures A structure can be viewed as an object
Contains no member functions (The structures used here have no member functions)
Contains multiple values of possibly different types
The multiple values are logically related as a single item
Example: A bank Certificate of Deposit (CD) has the following values: a balance an interest rate a term (months to maturity)

11. Remember this semicolon!
The CD Definition
The Certificate of Deposit structure can be defined as struct CDAccount { double balance; double interest_rate; int term; //months to maturity };
Keyword struct begins a structure definition
CDAccount is the structure tag or the structure’s type
Member names are identifiers declared in the braces
Remember this semicolon!

12. Using the Structure
Structure definition is generally placed outside any function definition
This makes the structure type available to all code that follows the structure definition
To declare two variables of type CDAccount: CDAccount my_account, your_account;
My_account and your_account contain distinct member variables balance, interest_rate, and term

13. Specifying Member Variables
Member variables are specific to the structure variable in which they are declared
Syntax to specify a member variable: Structure_Variable_Name . Member_Variable_Name
Given the declaration: CDAccount my_account, your_account;
Use the dot operator to specify a member variable my_account.balance my_account.interest_rate my_account.term

14. Using Member Variables
Member variables can be used just as any other variable of the same type
my_account.balance = 1000; your_account.balance = 2500;
Notice that my_account.balance and your_account.balance are different variables!
my_account.balance = my_account.balance + interest;
Display 10.1 (1)
Display 10.1 (2)
Display 10.2

15. Duplicate Names
Member variable names duplicated between structure types are not a problem.
super_grow.quantity and apples.quantity are different variables stored in different locations
struct FertilizerStock { double quantity; double nitrogen_content; }; FertilizerStock super_grow;
struct CropYield { int quantity; double size; }; CropYield apples;

16. Structures as Arguments
Structures can be arguments in function calls
The formal parameter can be call-by-value
The formal parameter can be call-by-reference
Example: void get_data(CDAccount& the_account);
Uses the structure type CDAccount we saw earlier as the type for a call-by-reference parameter

17. Structures as Return Types
Structures can be the type of a value returned by a function
Example: CDAccount shrink_wrap(double the_balance, double the_rate, int the_term) { CDAccount temp; temp.balance = the_balance; temp.interest_rate = the_rate; temp.term = the_term; return temp; }

18. Assignment and Structures
The assignment operator can be used to assign values to structure types
Using the CDAccount structure again: CDAccount my_account, your_account; my_account.balance = ; my_account.interest_rate = 5.1; my_account.term = 12; your_account = my_account;
Assigns all member variables in your_account the corresponding values in my_account

19. Initializing Structures
A structure can be initialized when declared
Example: struct Date { int month; int day; int year; };
Can be initialized in this way Date due_date = {12, 31, 2004};

20. Hierarchical Structures
Structures can contain member variables that are also structures
struct PersonInfo contains a Date structure
struct PersonInfo { double height; int weight; Date birthday; };
struct Date { int month;
int day;
int year; };

21. 10.2
Classes

22. Classes A class is a data type whose variables are objects
The definition of a class includes
Description of the kinds of values of the member variables
Description of the member functions
A class description is somewhat like a structure definition plus the member variables

23. Class Definitions A class definition includes
A description of the kinds of values the variable can hold
A description of the member functions
We will start by defining structures as a first step toward defining classes

24. What Is a Class? A class is a data type whose variables are objects
Some pre-defined data types you have used are
int
char
A pre-defined class you have used is
ifstream
You can define your own classes as well

25. Introduction to Classes
Class declaration format:
class className {
declaration; };
Notice the required ;

26. Access Specifiers Used to control access to members of the class.
Each member is declared to be either
public: can be accessed by functions
outside of the class or
private: can only be called by or accessed
by functions that are members of
the class

27. Class Example
class Square { private: int side; public: void setSide(int s) { side = s; } int getSide() { return side; } };
Access specifiers

28. More on Access Specifiers
Can be listed in any order in a class
Can appear multiple times in a class
If not specified, the default is private

29. 7.4 Creating and Using Objects
An object is an instance of a class
It is defined just like other variables
Square sq1, sq2;
It can access members using dot operator
sq1.setSide(5);
cout << sq1.getSide();
See pr7-01.cpp

30. Types of Member Functions
Acessor, get, getter function: uses but does not modify a member variable
ex: getSide
Mutator, set, setter function: modifies a member variable
ex: setSide

31. 7.5 Defining Member Functions
Member functions are part of a class declaration
Can place entire function definition inside the class declaration or
Can place just the prototype inside the class declaration and write the function definition after the class

32. What Is a Class? A class is a data type whose variables are objects
Some pre-defined data types you have used are
int
char
A pre-defined class you have used is
ifstream
You can define your own classes as well

33. Defining Member Functions Inside the Class Declaration
Member functions defined inside the class declaration are called inline functions
Only very short functions, like the one below, should be inline functions
int getSide()
{ return side; }

34. Inline Member Function Example
class Square {
private:
int side;
public:
void setSide(int s)
{ side = s; }
int getSide()
{ return side; } };
inline functions

35. Defining Member Functions After the Class Declaration
Put a function prototype in the class declaration
In the function definition, precede the function name with the class name and scope resolution operator (::)
int Square::getSide() {
return side; }
See pr7-02.cpp and pr7-03.cpp

36. Conventions and a Suggestion
Member variables are usually private
Accessor and mutator functions are usually public
Use ‘get’ in the name of accessor functions, ‘set’ in the name of mutator functions
Suggestion: calculate values to be returned in accessor functions when possible, to minimize the potential for stale data

37. Tradeoffs of Inline vs. Regular Member Functions
When a regular function is called, control passes to the called function
the compiler stores return address of call, allocates memory for local variables, etc.
Code for an inline function is copied into the program in place of the call when the program is compiled
This makes alarger executable program, but
There is less function call overhead, and possibly faster execution

38. A Class Example
To create a new type named DayOfYear as a class definition
Decide on the values to represent
This example’s values are dates such as July 4 using an integer for the number of the month
Member variable month is an int (Jan = 1, Feb = 2, etc.)
Member variable day is an int
Decide on the member functions needed
We use just one member function named output

39. Class DayOfYear Definition
class DayOfYear { public: void output( ); int month; int day; };
Member Function Declaration

40. Defining a Member Function
Member functions are declared in the class declaration
Member function definitions identify the class in which the function is a member
void DayOfYear::output() { cout << “month = “ << month << “, day = “ << day << endl; }

41. Member Function Definition
Member function definition syntax: Returned_Type Class_Name::Function_Name(Parameter_List) { Function Body Statements }
Example: void DayOfYear::output( ) { cout << “month = “ << month << “, day = “ << day << endl; }

42. The ‘::’ Operator ‘::’ is the scope resolution operator
Tells the class a member function is a member of
void DayOfYear::output( ) indicates that function output is a member of the DayOfYear class
The class name that precedes ‘::’ is a type qualifier

43. ‘::’ and ‘.’
‘::’ used with classes to identify a member void DayOfYear::output( ) { // function body }
‘.’used with variables to identify a member DayOfYear birthday; birthday.output( );

44. Calling Member Functions
Calling the DayOfYear member function output is done in this way: DayOfYear today, birthday; today.output( ); birthday.output( );
Note that today and birthday have their own versions of the month and day variables for use by the output function
Display 10.3 (1)
Display 10.3 (2)

45. Encapsulation Encapsulation is
Combining a number of items, such as variables and functions, into a single package such as an object of a class

46. Problems With DayOfYear
Changing how the month is stored in the class DayOfYear requires changes to the program
If we decide to store the month as three characters (JAN, FEB, etc.) instead of an int
cin >> today.month will no longer work because we now have three character variables to read
if(today.month == birthday.month) will no longer work to compare months
The member function “output” no longer works

47. Ideal Class Definitions
Changing the implementation of DayOfYear requires changes to the program that uses DayOfYear
An ideal class definition of DayOfYear could be changed without requiring changes to the program that uses DayOfYear

48. Fixing DayOfYear To fix DayOfYear
We need to add member functions to use when changing or accessing the member variables
If the program never directly references the member variables, changing how the variables are stored will not require changing the program
We need to be sure that the program does not ever directly reference the member variables

49. Public Or Private?
C++ helps us restrict the program from directly referencing member variables
private members of a class can only be referenced within the definitions of member functions
If the program tries to access a private member, the compiler gives an error message
Private members can be variables or functions

50. Private Variables
Private variables cannot be accessed directly by the program
Changing their values requires the use of public member functions of the class
To set the private month and day variables in a new DayOfYear class use a member function such as void DayOfYear::set(int new_month, int new_day) { month = new_month; day = new_day; }

51. Public or Private Members
The keyword private identifies the members of a class that can be accessed only by member functions of the class
Members that follow the keyword private are private members of the class
The keyword public identifies the members of a class that can be accessed from outside the class
Members that follow the keyword public are public members of the class

52. A New DayOfYear The new DayOfYear class demonstrated in Display 10.4…
Uses all private member variables
Uses member functions to do all manipulation of the private member variables
Member variables and member function definitions can be changed without changes to the program that uses DayOfYear
Display 10.4 (1)
Display 10.4 (2)

53. Using Private Variables
It is normal to make all member variables private
Private variables require member functions to perform all changing and retrieving of values
Accessor functions allow you to obtain the values of member variables
Example: get_day in class DayOfYear
Mutator functions allow you to change the values of member variables
Example: set in class DayOfYear

54. General Class Definitions
The syntax for a class definition is
class Class_Name { public: Member_Specification_1 Member_Specification_2 … Member_Specification_3 private: Member_Specification_n+1 Member_Specification_n+2 … };

55. Declaring an Object
Once a class is defined, an object of the class is declared just as variables of any other type
Example: To create two objects of type Bicycle:
class Bicycle { // class definition lines }; Bicycle my_bike, your_bike;

56. The Assignment Operator
Objects and structures can be assigned values with the assignment operator (=)
Example: DayOfYear due_date, tomorrow; tomorrow.set(11, 19); due_date = tomorrow;

57. Program Example: BankAccount Class
This bank account class allows
Withdrawal of money at any time
All operations normally expected of a bank account (implemented with member functions)
Storing an account balance
Storing the account’s interest rate
Display 10.5 ( 1)
Display 10.5 ( 3)
Display 10.5 ( 2)
Display 10.5 ( 4)

58. Calling Public Members
Recall that if calling a member function from the main function of a program, you must include the the object name: account1.update( );

59. Calling Private Members
When a member function calls a private member function, an object name is not used
fraction (double percent); is a private member of the BankAccount class
fraction is called by member function update void BankAccount::update( ) { balance = balance fraction(interest_rate)* balance; }

60. Constructors
A constructor can be used to initialize member variables when an object is declared
A constructor is a member function that is usually public
A constructor is automatically called when an object of the class is declared
A constructor’s name must be the name of the class
A constructor cannot return a value
No return type, not even void, is used in declaring or defining a constructor

61. Constructor Declaration
A constructor for the BankAccount class could be declared as: class BankAccount { public: BankAccount(int dollars, int cents, double rate); //initializes the balance to $dollars.cents //initializes the interest rate to rate percent …//The rest of the BankAccount definition };

62. Constructor Definition
The constructor for the BankAccount class could be defined as BankAccount::BankAccount(int dollars, int cents, double rate) { if ((dollars < 0) || (cents < 0) || ( rate < 0 )) { cout << “Illegal values for money or rate\n”; exit(1); } balance = dollars * cents; interest_rate = rate; }
Note that the class name and function name are the same

63. Calling A Constructor (1)
A constructor is not called like a normal member function: BankAccount account1; account1.BankAccount(10, 50, 2.0);

64. Calling A Constructor (2)
A constructor is called in the object declaration BankAccount account1(10, 50, 2.0);
Creates a BankAccount object and calls the constructor to initialize the member variables

65. Overloading Constructors
Constructors can be overloaded by defining constructors with different parameter lists
Other possible constructors for the BankAccount class might be BankAccount (double balance, double interest_rate); BankAccount (double balance); BankAccount (double interest_rate); BankAccount ( );

66. The Default Constructor
A default constructor uses no parameters
A default constructor for the BankAccount class could be declared in this way class BankAccount { public: BankAccount( ); // initializes balance to $ // initializes rate to 0.0% … // The rest of the class definition };

67. Default Constructor Definition
The default constructor for the BankAccount class could be defined as BankAccount::BankAccount( ) { balance = 0; rate = 0.0; }
It is a good idea to always include a default constructor even if you do not want to initialize variables

68. Calling the Default Constructor
The default constructor is called during declaration of an object
An argument list is not used BankAccount account1; // uses the default BankAccount constructor BankAccount account1( ); // Is not legal
Display 10.6 (1)
Display 10.6 (2)
Display 10.6 (3)

69. Initialization Sections
An initialization section in a function definition provides an alternative way to initialize member variables
BankAccount::BankAccount( ): balance(0), interest_rate(0.0); { // No code needed in this example }
The values in parenthesis are the initial values for the member variables listed

70. Parameters and Initialization
Member functions with parameters can use initialization sections BankAccount::BankAccount(int dollars, int cents, double rate) : balance (dollars * cents), interest_rate(rate) { if (( dollars < 0) || (cents < 0) || (rate < 0)) { cout << “Illegal values for money or rate\n”; exit(1); } }
Notice that the parameters can be arguments in the initialization

71. Member Initializers
C++11 supports a feature called member initialization
Simply set member variables in the class
Ex: class Coordinate {
private:
int x=1;
int y=2;
... };
Creating a Coordinate object will initialize its x variable to 1 and y to 2 (assuming a constructor isn’t called that sets the values to something else)

72. Constructor Delegation
C++11 also supports constructor delegation. This lets you have a constructor invoke another constructor in the initialization section.
For example, make the default constructor call a second constructor that sets X to 99 and Y to 99:
Coordinate::Coordinate() : Coordinate(99,99)
{ }

73. Section 10.2 Conclusion Can you
Describe the difference between a class and a structure?
Explain why member variables are usually private?
Describe the purpose of a constructor?
Use an initialization section in a function definition?

74. 10.3
Abstract Data Types

75. Abstract Data Types
A data type consists of a collection of values together with a set of basic operations defined on the values
A data type is an Abstract Data Type (ADT) if programmers using the type do not have access to the details of how the values and operations are implemented

76. Classes To Produce ADTs
To define a class so it is an ADT
Separate the specification of how the type is used by a programmer from the details of how the type is implemented
Make all member variables private members
Basic operations a programmer needs should be public member functions
Fully specify how to use each public function
Helper functions should be private members

77. ADT Interface The ADT interface tells how to use the ADT in a program
The interface consists of
The public member functions
The comments that explain how to use the functions
The interface should be all that is needed to know how to use the ADT in a program

78. ADT Implementation
The ADT implementation tells how the interface is realized in C++
The implementation consists of
The private members of the class
The definitions of public and private member functions
The implementation is needed to run a program
The implementation is not needed to write the main part of a program or any non-member functions

79. ADT Benefits
Changing an ADT implementation does require changing a program that uses the ADT
ADT’s make it easier to divide work among different programmers
One or more can write the ADT
One or more can write code that uses the ADT
Writing and using ADTs breaks the larger programming task into smaller tasks

80. Program Example The BankAccount ADT
In this version of the BankAccount ADT
Data is stored as three member variables
The dollars part of the account balance
The cents part of the account balance
The interest rate
This version stores the interest rate as a fraction
The public portion of the class definition remains unchanged from the version of Display 10.6
Display 10.7 (1)
Display 10.7 (3)
Display 10.7 (2)

81. Interface Preservation
To preserve the interface of an ADT so that programs using it do not need to be changed
Public member declarations cannot be changed
Public member definitions can be changed
Private member functions can be added, deleted, or changed

82. Information Hiding
Information hiding was refered to earlier as writing functions so they can be used like black boxes
ADT’s implement information hiding because
The interface is all that is needed to use the ADT
Implementation details of the ADT are not needed to know how to use the ADT
Implementation details of the data values are not needed to know how to use the ADT

83. Section 10.3 Conclusion Can you Describe an ADT?
Describe how to implement an ADT in C++?
Define the interface of an ADT?
Define the implementation of an ADT?

84. Object Oriented Programming
Review from Chapter 1
Object Oriented Programming

85. Object Oriented Programming
Abbreviated OOP
Used for many modern programs
Program is viewed as interacting objects
Each object contains algorithms to describe its behavior
Program design phase involves designing objects and their algorithms

86. OOP Characteristics Encapsulation Information hiding
Objects contain their own data and algorithms
Inheritance
Writing reusable code
Objects can inherit characteristics from other objects
Polymorphism
A single name can have multiple meanings depending on its context

87. Object-Oriented Programming Terminology
object: software entity that combines data and functions that act on the data in a single unit
attributes: the data items of an object, stored in member variables
member functions (methods): procedures/ functions that act on the attributes of the class

88. More Object-Oriented Programming Terminology
data hiding: restricting access to certain members of an object. The intent is to allow only member functions to directly access and modify the object’s data
encapsulation: the bundling of an object’s data and procedures into a single entity

89. Why Hide Data?
Protection – Member functions provide a layer of protection against inadvertent or deliberate data corruption
Need-to-know – A programmer can use the data via the provided member functions. As long as the member functions return correct information, the programmer needn’t worry about implementation details.

90. 7.2 Object-Oriented Programming
Procedural programming uses variables to store data, and focuses on the processes/ functions that occur in a program. Data and functions are separate and distinct.
Object-oriented programming is based on objects that encapsulate the data and the functions that operate on it.

91. Object Example Square object’s data item: side
Member variables (attributes)
int side;
Member functions
void setSide(int s)
{ side = s; }
int getSide()
{ return side; }
Square object’s data item: side
Square object’s functions: setSide - set the size of the side of the square, getSide - return the size of the side of the square

92. Introduction to Inheritance
10.4
Introduction to Inheritance

93. Inheritance Inheritance refers to derived classes
Derived classes are obtained from another class by adding features
A derived class inherits the member functions and variables from its parent class without having to re-write them
Example
In Chapter 6 we saw that the class of input-file streams is derived from the class of all input streams by adding member functions such as open and close
cin belongs to the class of all input streams, but not the class of input-file streams

94. Inheritance Example Natural hierarchy of bank accounts
Most general: A Bank Account stores a balance
A Checking Account “IS A” Bank Account that allows customers to write checks
A Savings Account “IS A” Bank Account without checks but higher interest
Accounts are more specific as we go down the hierarchy
Each box can be a class

95. Inheritance Relationships
The more specific class is a derived or child class
The more general class is the base, super, or parent class
If class B is derived from class A
Class B is a derived class of class A
Class B is a child of class A
Class A is the parent of class B
Class B inherits the member functions and variables of class A

96. Defining Derived Classes
Give the class name as normal, but add a colon and then the name of the base class
Objects of type SavingsAccount can access member functions defined in SavingsAccount or BankAccount
class SavingsAccount : public BankAccount { … }
Display 10.9 (1-3)

97. Section 10.4 Conclusion Can you Define object? Define class?
Describe the relationship between parent and child classes?
Describe the benefit of inheritance?

98. Chapter End

99. Display (1/2)
Back
Next

100. Display 10.1 (2/2)
Back
Next

101. Display 10.2
Back
Next

102. Display 10.3 (1/2)
Back
Next

103. Display 10.3 (2/2)
Back
Next

104. Display (1/2)
Back
Next

105. Display 10.4 (2/2)
Back
Next

106. Display 10.5 (1/4)
Back
Next

107. Display 10.5 (2/4)
Back
Next

108. Display 10.5 (3/4)
Back
Next

109. Display 10.5 (4/4)
Back
Next

110. Display (1/3)
Back
Next

111. Display 10.6 (2/3)
Back
Next

112. Display (3/3)
Back
Next

113. Display 10.7 (1/3)
Back
Next

114. Display 10.7 (2/3)
Back
Next

115. Display 10.7 (3/3)
Back
Next

116. Display 10.8
Back
Next

117. Display 10.9 (1/3)
Back
Next

118. Display 10.9 (2/3)
Back
Next

119. Display 10.9 (3/3)
Back
Next

122. Introduction to Computers and C++ Programming
Chapter 1
Introduction to Computers and
C++ Programming

123. Chapter 7: Introduction to Classes and Objects
Starting Out with C++ Early Objects
Eighth Edition
by Tony Gaddis, Judy Walters, and Godfrey Muganda

124. Topics 7.1 Abstract Data Types 7.2 Object-Oriented Programming
7.3 Introduction to Classes
7.4 Creating and Using Objects
7.5 Defining Member Functions
7.6 Constructors
7.7 Destructors
7.8 Private Member Functions

125. Topics (Continued)
7.9 Passing Objects to Functions 7.10 Object Composition 7.11 Separating Class Specification, Implementation, and Client Code

126. 7.1 Abstract Data Types
Structures/Classes that are defined by the operations that are performed by/on it.
Have no implementation defined
“interface contract” that the object provides

127. 7.1 Abstract Data Types Programmer-created data types that specify
legal values that can be stored
operations that can be done on the values
The user of an abstract data type (ADT) does not need to know any implementation details (e.g., how the data is stored or how the operations on it are carried out)

128. Abstraction in Software Development
Abstraction allows a programmer to design a solution to a problem and to use data items without concern for how the data items are implemented
This has already been encountered in the book:
To use the pow function, you need to know what inputs it expects and what kind of results it produces
You do not need to know how it works

129. Abstraction and Data Types
Abstraction: a definition that captures general characteristics without details
ex: An abstract triangle is a 3-sided polygon. A specific triangle may be scalene, isosceles, or equilateral
Data Type: defines the kind of values that can be stored and the operations that can be performed on it

130. 7.6 Constructors
A constructor is a member function that is often used to initialize data members of a class
Is called automatically when an object of the class is created
It must be a public member function
It must be named the same as the class
It must have no return type
See pr7-04.cpp and pr7-05.cpp

131. Constructor – 2 Examples
Inline:
class Square {
. . .
public:
Square(int s)
{ side = s; } };
Declaration outside the class:
Square(int); //prototype
//in class
Square::Square(int s)
side = s; }

132. Overloading Constructors
A class can have more than 1 constructor
Overloaded constructors in a class must have different parameter lists
Square();
Square(int);
See pr7-06.cpp

133. The Default Constructor
Constructors can have any number of parameters, including none
A default constructor is one that takes no arguments either due to
No parameters or
All parameters have default values
If a class has any programmer-defined constructors, it must have a programmer- defined default constructor

134. Default Constructor Example
class Square { private: int side; public: Square() // default { side = 1; } // constructor // Other member // functions go here };
Has no
parameters

135. Another Default Constructor Example
class Square { private: int side; public: Square(int s = 1) // default { side = s; } // constructor // Other member // functions go here };
Has parameter
but it has a default value

136. Invoking a Constructor
To create an object using the default constructor, use no argument list and no ()
Square square1;
To create an object using a constructor that has parameters, include an argument list
Square square1(8);

137. 7.7 Destructors
Is a public member function automatically called when an object is destroyed
The destructor name is ~className, e.g., ~Square
It has no return type
It takes no arguments
Only 1 destructor is allowed per class
(i.e., it cannot be overloaded)
See pr7-07.cpp

138. 7. 8 Private Member Functions
A private member function can only be called by another member function of the same class
It is used for internal processing by the class, not for use outside of the class
See pr7-08.cpp

139. 7.9 Passing Objects to Functions
A class object can be passed as an argument to a function
When passed by value, function makes a local copy of object. Original object in calling environment is unaffected by actions in function
When passed by reference, function can use ‘set’ functions to modify the object.
See pr7-09.cpp

140. Notes on Passing Objects
Using a value parameter for an object can slow down a program and waste space
Using a reference parameter speeds up program, but allows the function to modify data in the parameter

141. Notes on Passing Objects
To save space and time, while protecting parameter data that should not be changed, use a const reference parameter
void showData(const Square &s)
// header
In order to for the showData function to call Square member functions, those functions must use const in their prototype and header:
int Square::getSide() const;

142. Returning an Object from a Function
A function can return an object
Square initSquare(); // prototype
s1 = initSquare(); // call
The function must define a object
for internal use
to use with return statement

143. Returning an Object Example
Square initSquare() {
Square s; // local variable
int inputSize;
cout << "Enter the length of side: ";
cin >> inputSize;
s.setSide(inputSize);
return s; }
See pr7-10.cpp

144. 7.10 Object Composition
Occurs when an object is a member variable of another object.
It is often used to design complex objects whose members are simpler objects
ex. (from book): Define a rectangle class. Then, define a carpet class and use a rectangle object as a member of a carpet object.
See pr7-11.cpp

145. Object Composition, cont.

146. Chapter 7: Introduction to Classes and Objects
Starting Out with C++ Early Objects
Eighth Edition
by Tony Gaddis, Judy Walters, and Godfrey Muganda

147. 7.11 Separating Class Specification, Implementation, and Client Code
Separating class declaration, member function definitions, and the program that uses the class into separate files is considered good design

148. Using Separate Files
Place class declaration in a header file that serves as the class specification file. Name the file classname.h (for example, Square.h)
Place member function definitions in a class implementation file. Name the file classname.cpp (for example, Square.cpp)This file should #include the class specification file.
A client program (client code) that uses the class must #include the class specification file and be compiled and linked with the class implementation file.
See pr7-12.cpp, Rectangle.cpp, and Rectangle.h

149. Include Guards Used to prevent a header file from being included twice
Format:
#ifndef symbol_name
#define symbol_name
(normal contents of header file)
#endif
symbol_name is usually the name of the header file, in all capital letters:
#ifndef SQUARE_H
#define SQUARE_H
. . .

150. What Should Be Done Inside vs. Outside the Class
Class should be designed to provide functions to store and retrieve data
In general, input and output (I/O) should be done by functions that use class objects, rather than by class member functions
See Rectangle.h, Rectangle.cpp, and pr7-12.cpp

151. Chapter 7: Introduction to Classes and Objects
Starting Out with C++ Early Objects
Eighth Edition
by Tony Gaddis, Judy Walters, and Godfrey Muganda

152. 7.14 Introduction to Object-Oriented Analysis and Design
Object-Oriented Analysis: that phase of program development when the program functionality is determined from the requirements
It includes
identification of objects and classes
definition of each class's attributes
identification of each class's behaviors
definition of the relationship between classes

153. Identify Objects and Classes
Consider the major data elements and the operations on these elements
Candidates include
user-interface components (menus, text boxes, etc.)
I/O devices
physical objects
historical data (employee records, transaction logs, etc.)
the roles of human participants

154. Define Class Attributes
Attributes are the data elements of an object of the class
They are necessary for the object to work in its role in the program

155. Define Class Behaviors
For each class,
Identify what an object of a class should do in the program
The behaviors determine some of the member functions of the class

156. Relationships Between Classes
Possible relationships
Access ("uses-a")
Ownership/Composition ("has-a")
Inheritance ("is-a")

157. Finding the Classes Technique:
Write a description of the problem domain (objects, events, etc. related to the problem)
List the nouns, noun phrases, and pronouns. These are all candidate objects
Refine the list to include only those objects that are relevant to the problem

158. Determine Class Responsibilities
What is the class responsible to know?
What is the class responsible to do?
Use these to define some of the member functions

159. Object Reuse
A well-defined class can be used to create objects in multiple programs
By re-using an object definition, program development time is shortened
One goal of object-oriented programming is to support object reuse

160. Chapter 7: Introduction to Classes and Objects
Starting Out with C++ Early Objects
Eighth Edition
by Tony Gaddis, Judy Walters, and Godfrey Muganda