OOP in C++

By: Saif Bashar

Introduction to Classes

2017

www.saifacademy.com

Updated on 11-12

Object Oriented Programming

› New way of looking at things

› Large programs became interacting objects

› Everything is an object that belongs to a class

› Classes developed and tested independently

› Separating the implementation from the interface

Object Oriented Programming

Objects have some attributes

Objects have some functionalityObject

Attributes

Methods

Object Oriented Programming

Objects have some attributes

Objects have some functionality

Class: Player

Object: CR7

Object: Messi

NameNationalityPositionRun ()Skills ()Shoot ()Pass ()Dribble ()Header ()

RonaldoPortugalForward908095808599

MessiArgentinaForward908593909080

Pillars of OOP

Polymorphism

Inheritance

OOPEncapsu

lation

C vs C++

int char float double bool for if else switch case default while do break continue struct auto const enum

extern goto long short signed unsigned sizeof

return union static register typedef void

volatile

new

private

public

protected

template

operator

class

delete

asmfriend

catch

try

inline

thisthrow

virtual

C has 33 keyword

C++ has 49 keyword

New Keywords added in new versions

Object Oriented Programming

› Classes are user defined types - UDT

› Objects are instances of a class

› Objects contains data and functions

› Data are called (data members)

› Functions are called (member functions) or (methods)

Class Definitionclass className {

private:

data1;

data2;

data3;

public:

function1(){}

function2(){}

function3(){}

protected:

};

Data members

Member functions (Methods)

Class Rectangle

class rectangle {

private:

int width;

int length;

public:

int area(){

return (width *length);

}

void setValues(int x, int y){

width = x;

length = y;

}

};

int main () {

rectangle r1;

r1.setValues(3,5);

cout<<r1.area();

rectangle r2;

r2.setValues(4,6);

cout<<r2.area();

return 0;

}

Example

Notes on rectangle class

› Data members should remain private

› Data members can be accessed only by class methods

› We specify some methods to be public

› Public methods can be called from outside the class

OOP

Encapsulation

The details of the class implementation are hidden and contained inside the class

It is also called data hiding

Class Constructor

› Initialize the class data members

› Reserve a space in memory for the object

› Has the same name of the class

› Has no return type

› Can be overloaded

› Called automatically when we declare an object

Class Rectangle

class rectangle {

private:

int width;

int length;

public:

int area(){

return (width *length);

}

rectangle(int x, int y){

width = x;

length = y;

}

};

int main () {

rectangle r1 (3,5);

cout<<r1.area();

rectangle r2(4,6);

cout<<r2.area();

return 0;

}

Example

Class Destructor

› Destroy the object

› Free the memory occupied by the object

› Has the same name of the class preceded with (~)

› Has no return type

› Has no arguments

› Can not be overloaded

› Called automatically when the object’s scope ends

Class Rectangle

class rectangle {

private:

int width;

int length;

public:

int area(){

return (width * length);}

rectangle(int x, int y){

width = x;

length = y;}

~rectangle(){

cout<<“Object is destroyed”;}

};

int main () {

rectangle r1 (3,5);

cout<<r1.area();

rectangle r2(4,6);

cout<<r2.area();

return 0;

}

Example

Class Rectangle

class rectangle {

private:

int *width; int *length;

public:

int area(){

return (*width * *length);}

rectangle(int x, int y){

width = new int;

length = new int;

*width = x;

*length = y;}

~rectangle(){

delete width; delete length; }

};

int main () {

rectangle r1 (3,5);

cout<<r1.area();

rectangle r2(4,6);

cout<<r2.area();

return 0;

}

Example

Building a Complete Class

Definition

Data Members

Member Functions

Constructor

Destructor

Object

Class

OOP

File Separation

Classes usually separated into two files:

- The header file (contains the class definition)

- The Implementation file (contains the class implementation)

Scope Resolution Operator

› We can use the scope resolution operator

› To define the methods outside the class

› The method prototype must be included in the class definition

Class Rectangle

class rectangle {

private:

int width;

int length;

public:

int area();

rectangle(int, int);

~rectangle();

};

int rectangle::area(){

return (width * length);}

rectangle::rectangle(int x,

int y){ width = x;

length = y;}

rectangle::~rectangle(){

cout<<“Object is

destroyed”;}

Example

class rectangle {

private:

int width;

int length;

public:

int area();

rectangle(int, int);

~rectangle();

};

#include ”rectangle.h”

int rectangle::area(){

return (width * length);}

rectangle::rectangle(int x,

int y){ width = x;

length = y;}

rectangle::~rectangle(){

cout<<“Object is

destroyed”;}

rectangle.h rectangle.cpp