Lecture 02

Fundamentals

of Object-Oriented

Programming

What Are Objects?

Software objects model real-world objects or abstract concepts. dog, bicycle, queue

Real-world objects have states and behaviors. Dogs' states: name, color, breed, hungry Dogs' behaviors: barking, fetching

How do software objects implement real-world objects? Use variables/data to implement states. Use methods/functions to implement behaviors.

An object is a software bundle of variables and related methods.

Software ObjectVisual Representation

Instance Variables Vs Instance Methods

Software BicycleVisual Representation

What Are Classes?

• A class is a blueprint or prototype defining the variables and methods common to all objects of a certain kind.

• An object is an instance of a certain class.

• After you have created a class, you must create an instance of it before you can use.

• Class variables and class methods.

What Are Messages?

Software objects interact and communicate with each other by sending messages to each other.

Components Of A Message

The object to whom the message is addressed (YourBicycle)

The name of the method to perform (changeGears) Any parameters needed by the method (lowerGear)

O-O Principles

• Abstraction - take only important information

• Encapsulation - hiding or combine data and operations on data in a single unit.

• Inheritance - create new objects from existing objects.

• Polymorphism-the ability to use the same expression to denote different operations.

Encapsulation

• The objects' variables make up the center of the object.

• Methods surround and hide the object's center from other objects.

• Benefit of encapsulation: Modularity & Information Hiding.

• For implementation or efficiency reasons, an object may wish to expose some of its variables or hide some of its methods.

Inheritance

• Inheritance allows classes to be defined in terms of other classes.

• Each subclass inherits variables and methods from its superclass.

• Subclasses can add variables and methods to the ones they inherit from the superclass.

• Subclasses can also override inherited methods and provide specialized implementations for those methods.

Class Hierarchy(Inheritance Hierarchy)

Superclass vs Subclass. Base Class vs Derived Class.

Polymorphism and Overloading

• Polymorphism allows the use of operators or functions in different ways, depending on the data they are operating on.

• When an existing operator (eg. + or =) is given the capability to operate on a new data type, it is said to be overloaded.

• Overloading is a kind of polymorphism; it is also an important feature of OOP.

   Example of operator overloading and polymorphism)• the + operator know how to treat an integer and a float

differently.

Benefits of OOPReusability

• Once written, created, and debugged, a class can be distributed to other programmers for use in their own programs.

• Reusability facilitates component-based software design and implementation.

• A programmer can also take an existing class and, without modifying it, add additional features and capabilities to it.

Benefits of OOPCreating New Data Types

• Objects and classes give the programmer a convenient way to construct new data types.

• Many features of C++ are intended to facilitate the creation of new data types.

• The ability to create new data types leads to extensible languages and programs.

• In C++, new data types can be built on top of existing (system or user-defined) data types.

C++ Program Structure

Header files

preprocessor statements

class

{ …..

}

main( )

{ ……

}

#include <iostream.h>

int main( ) // VOID

{

cout << “Welcome to C++”;

return 0;

}

Variable declarations & valid C++ statements

Data Members and Member Functions

Example 2

#include <iostream.h>

int main ( )

{ int a , b, c, sum =0;

cout << “ enter a value “<<endl;

cin >> a;

cout << “ enter b value “<<endl;

cin >> b;

cout << “ enter c value “<<endl;

cin >> c;

Sum = a + b + c;

cout << “ the sum is “<< sum;

OTHER DATA TYPESChar

int long int

floatdouble

Input / Output

Cout - used for printing out the output

Syntax :

Cout << “Message if needed”<< variablename;

<< is called the insertion operator.

Cin - used for getting a input from the keyboard

Syntax:

Cin >> variable name;

>> is called the extraction operator

Other Points

Remark statement - it is a non executable statement

used for documentation

// or /* statements */

escape sequences:

\n - new line

\t - horizontal tab

\r - carriage return

\a - bell

\\ - back slash \” - double quotations