This document discusses object oriented programming using C++. It begins by defining OOP and its key features like encapsulation, inheritance, and polymorphism. It then discusses objects, classes, properties, functions, and how to declare classes with access specifiers. The document provides examples of creating objects from classes and accessing class members using objects. It also discusses defining member functions outside of classes. Finally, it provides exercises for readers to practice implementing classes with data members and member functions.

1. LAB 4: OBJECT ORIENTED
PROGRAMMING USING C++
ENG. MOHAMMED AL-OBAIDI
UNIVERSITY OF SANA’A
FACILITY OF ENGINEERING
MECHATRONICS
DEPARTMENT

2. OOP
⚫ It is programming technique in which programs are
written on the basis of objects
⚫ It is a powerful technique to develop software.
⚫ It is used to analyze and design the application in terms of
objects.
⚫ It deals with data and the procedures as a single unit
⚫ Each object is responsible to initialize and destroy itself.

3. FEATURES OF OBJECT-ORIENTED
PROGRAMMING
 Data abstraction
The procedure used to define a class from objects.
 Encapsulation
A technique for Information Hiding.
 Inheritance
It allows to define a class in terms of another class, which makes it easier
to create and maintain an application.
 Polymorphism
The word polymorphism means having many forms.
Typically, polymorphism occurs when there is a hierarchy of classes and
they are related by inheritance.

4. EFFECTS OF OO METHODOLOGY ON
SOFTWARE DESIGN
 Maintenance
 Extensibility
 Reusability

5. OBJECTS
o Object represents an entity in the real world
o Identified by its name
o It consists of two things:
⯍Properties:
⯍Functions
Characteristics of an object
Actions performed by the object
o Everything is an object
o Systems are composed of objects

6. OBJECTS
■ An object is an instance of a class.
■ An object is a class variable.
■ Is can be uniquely identified by its name.
■ Every object have a state which is represented by the
values of its attributes. These state are changed by
function which applied on the object.

7. ⚫ Everything is an object
⚫ A student, a professor
⚫ A desk, a chair, a classroom, a building
⚫ A university, a city, a country
⚫ The world, the universe
⚫ A subject such as CS, IS, Math, History, …
⚫ Systems are composed of objects
⚫ An educational system
⚫ An economic system
⚫ An information system
⚫ A computer system

8. PROPERTIES OF OBJECTS
⚫ Characteristics of an object are known as Properties or
attributes of the object
⚫Each object has its own properties
Example:
⚫ If “Person” is an object, it has following properties
 Name
 Age
 Weight
Object: Car
Properties: Model, Color, Price

9. FUNCTIONS OF AN OBJECT
⚫Tasks or actions performed by the object are known
as functions or methods.

10. CLASSES
⚫ Collection of objects with same
properties and functions
⚫ Use to define characteristics of the object
⚫ Used as a model for creating different
objects of same type
⚫ Each object of a class is known as an
instance of the class
⚫ A Class is a user defined data type to implement an abstract
object. Abstract means to hide the details. A Class is a
combination of data and functions.

11. DECLARING A CLASS
⚫ Keyword “class” is used to declare a class
⚫ The body of the class is contained within a set of braces,
{ } ; (notice the semi-colon).
Syntax:
class identifier
{
//Body of the class
};
Class: is the keyword
Identifier: name of the class to be declared

12. ACCESS SPECIFIERS
⚫It specifies the access level of the class members
⚫Two common access specifiers are:
⚫ Private:
Restrict the use of the class members within the class. It is the default
access specifier. It is used to protect the data members from direct
access from outside the class. Data Member are normally declared with
private access specifier.
⚫ Public
It allows the user to access members within the class as well as outside
the class. It can be accessed from anywhere in the program. Member
functions are normally declared with public access specifier.

13. ACCESS SPECIFIERS
⚫Usually, the data members of a class are declared in
the private: section of the class and the member
functions are in public: section.
⚫Data member or member functions may be public,
private or protected.
⚫Member access specifiers
■ public:
■ can be accessed outside the class directly.
■ The public stuff is the interface.

14. ACCESS SPECIFIERS
⚫Member access specifiers
■ private:
■ Accessible only to member
functions of class.
■ Private members and
methods are for internal use
only.
■ Protected means data member
and member functions can be
used in the same class and its
derived class (at one level) (not
inmain function).

15. class class_name
{
private:
…
…
…
public:
…
…
…
};
Public members or methods
private members or methods
class Circle
{
private:
double radius;
public:
void setRadius(double r);
double getDiameter();
double getArea();
double getCircumference();
};
and retrieve its value directly. The
class methods are responsible for
that only.
They are accessible from outside
the class, and they can access the
member (radius)

16. CREATING OBJECTS
⚫ Class is simply a model or prototype for creating objects.
⚫ It is like a new data type that contains both data and
functions.
⚫ Object is created in the same way as other variables are
created.
⚫ Object is also known as instance of a class.
⚫ Process of creating an object is also called instantiation.
Syntax:
class_name object_name;
Class_name: name of the class whose type of object is to be created
Object_name: object to be created.

17. ACCESSING CLASS MEMBERS
⚫Member functions are used to manipulate data
members of a class.
⚫We can access
⚫class attributes
⚫class methods
⚫We need an object to access instance variables
Syntax:
Object_name.data;
Object_name.function();
Object_name: name of object whose member function is to be executed
Function: It is the member function that is need to be executed.

18. ACCESSING CLASS MEMBERS
If we have a pointer to an object (member of pointer
operator)
• Dereference the pointer then use the dot operator.
Account *moh= new Account ();
(* moh). balance;
(* moh). deposit (1000.00);
• Or use the member of pointer operator (arrow
operator)
Account * moh = new Account();
moh >balance;

19. WRITE A PROGRAM
THAT DECLARES A
CLASS WITH A DATA
MEMBER AND TWO
MEMBER
FUNCTIONS
OUTPUT:
enter number 10
the value of n= 10

20. DEFINING MEMBER FUNCTIONS
OUTSIDE CLASS
⚫ Functions declaration are specified within the class (implicitly
inline)
⚫ Function definition is specified outside the class
⚫ Scope resolution operator :: is used in function declaration if
the function is defined outside the class.
Syntax:
Return_type class_name :: function_name(parameters)
{
function body
}
Return_type type of value to be returned by function
class_name class name to which function belongs
:: scope resoltion operator
function_name name of funtio to be defined

21. EXERCISE
#include <iostream>
using namespace std;
class Lab4 {
public:
int x = 20; double y = 3.6 ; string m = "Lab 4" ;
void display( )
{ cout<<"x= "<<x<<endl;
cout<<"y= "<<y<<endl; cout<<"m= "<<m<<endl; cout<<"z= "<<z<<endl;
} //end of display function
private:
float z = 2.4;
}; //end of class Lab2
int main()
{ Lab4 a ; // creating an object
Lab4 a2; // creating an object
cout << "by using a : " << endl;
a.display();
cout << "by using a2 : " << endl;
a2.display();
a.m=“Mohammed";
a.x=4; a2.y=80.8;
cout << "After changing the values:" << endl;
cout << "by using a : " << endl;
a.display();
cout << "by using a2 : " << endl;
a2.display();
return 0; }
Lab3
+ x : int
+ y : double
+ m : string
- z : float
+ display ( ) : void

22. EXERCISE
#include <iostream>
using namespace std;
class A2 {
public:
void disp( )
{ cout<<"Class A2"<<endl; }
}; //end of class A2
int main()
{ A2 a1;
a1.disp();
A2 *a2;
a2->disp();
return 0;
} //end of main function

23. EXERCISE
Exercise 1:
#include <iostream>
using namespace std;
int main()
{
cout << "Enter the width, please:" << endl;
double a ;
cin>>a;
cout << "Enter the height, please:" << endl;
double b ;
cin>>b;
Cal c;
c.setnum(a,b);
cout<<"The area is: "<<c.getnum()<<endl;
return 0;
}
Exercise 1 contains the main
function (don’t modify this
function for any reason). You
have to write Cal class. In
this class there are 3
functions:
1 setnum to accept the
width and height.
2 cal_area to calculate
the area of rectangle.
3 getnum to return the
value of the area.