Chapter 8

1
Chapter 8 Classes and Objects
2
Advantages of Using Objects

• Classes form tightly knit group of functions
• Distinct program boundaries
• More reliable large programs
• Reduces amount of programming done from scratch

Lesson 8.1
3
struct

• Data type created by grouping other data types
• Contains data members
• Defined by programmer derived data type
• Declares space for all data members

Lesson 8.1
4
Syntax

• struct fluid
• public
• char initial
• double temp, density, velocity

Lesson 8.1
5
Declaring struct Variables

• Use struct name followed with names of variables
• Example
• Fluid water, oil

Lesson 8.1
6
Assigning Values to Data Members

• Use dot operator with variable name to store and
  access values
• Examples
• water.density 9.81
• oil.density water.density

Lesson 8.1
7
Class

• Class is a type
• Aggregation of both data and functions
• General form

class Class_name private
private_members public
public_members
Lesson 8.2
8
Class Members

• Listed as in ordinary declarations
• Type and identifier in sequence
• Class definition does NOT reserve memory for
  class members
• Memory reserved when class declared
• Cannot use storage class specifiers auto, extern
  or register
• Can be objects of other classes

Lesson 8.2
9
Access Specifiers

• Private
• Restricts access of data to member functions
• member data cannot be accessed directly from main
• Public
• Allows member function to be called from main or
  any other function in program

Lesson 8.2
10
Member Function Definitions

• Those not included inside class definition
• Require class name and scope resolution operator
  () to immediately precede function name

type class_name function header
type variable statements return
(value )
Lesson 8.2
11
Objects

• New memory reserved for each data member of class
  when object declared
• Encapsulation
• Link between data and functions of object
• data hiding data access restricted to member
  functions
• Classes create programming units with distinct
  boundaries
• Instantiation
• Declaration of objects of a particular class
  (instances)

Lesson 8.2
12
Function Calls

• Each member function called must be associated
  with an object
• Example object_name . function_name
• object_name called invoking object

Function call
ob1 . calc_area (left_limit,
right_limit) double Parabola calc_area
(double x1, double x2)
Function header
Lesson 8.2
13
Constructor Function

• Class member function executed automatically upon
  declaration of object
• Frequently used to initialize values of data
  members
• Can be called just Constructor

Lesson 8.3
14
Constructor Characteristics

• Name identical to class name
• Does not return a value
• Has public access
• May or may not have arguments

Lesson 8.3
15
Constructor Function Form
class Name private
type data_member public
Name ( ) type
function_member ( )
Lesson 8.3
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Construction Function Definition
Name Name ( ) data_member
value
Lesson 8.3
17
Constructor Functions - Arguments

• Cannot return a value but can receive value
  through argument list
• Function can assign value to data member
• Passing a value to a constructor

Weather_station (int) Weather_station station
(5) Weather_station Weather_station (int
wind_speed_var)
Lesson 8.4
18
Initializing Data Member with Constructor

• Initialization list which follows single colon
  written after header
• Data member name and temporary storage variable
  name (enclosed in parentheses)
• General Form

Class Class (type dummy)
data_member (dummy)
data member set equal to valuepassed to dummy
Lesson 8.4
19
Explicitly Calling a Constructor Function

• Cannot call like other member functions
• Can call constructor a second time for that
  object using an assignment statement

station1 Weather_station (10)
Right side creates nameless object that is
assigned to station1
Lesson 8.4
20
Overloading Constructor Function

• Can have two or more constructor functions in
  class definition
• Default copy constructor automatically executed
  when one object declared to be identical to
  another
• Distinguishable in terms of number or type of
  arguments

Lesson 8.5
21
Overload Declarations

• Same name with different argument lists
• Example

Microwave_instruction ( ) Microwave_instruction
(int) Microwave_instruction (int, int)
Lesson 8.5
22
Summary
Learned how to

• Define a class
• Use an object
• Select class data members
• Select class function members
• Create a constructor function
• Create overloaded constructor functions