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Abstraction

Data abstraction refers to providing only essential information to the outside world and hiding their background details.
Real life example of a TV, which you can turn on and off, change the channel, adjust the volume, and add external components such as speakers, VCRs, and DVD players, BUT you do not know its internal details, that is, how it receives signals over the air or through a cable, how it translates them, and finally displays them on the screen.

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Abstraction

In C++, classes provides great level of data abstraction. They provide sufficient public methods to the outside world to play with the functionality of the object and to manipulate object data, i.e., state without actually knowing how class has been implemented internally.
In C++, we use classes to define our own abstract data types (ADT). You can use the cout object of class ostream to stream data to standard output .
you don't need to understand how cout displays the text on the user's screen. You need to only know the public interface and the underlying implementation of ‘cout’ is free to change.

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Encapsulation

Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse.
Data encapsulation led to the important OOP concept of data hiding.
Data encapsulation is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

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Inheritance

Feature that enables the characteristics or properties of a parent to reach its child
C++ supports inheritance
A class can inherit one or more classes
Inherited class is called as parent class or super class or base class
Class that inherits a parent class is called as child class or sub class or derived class

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Polymorphism

Poly – Many
Morph – Form
Polymorphism is the characteristic that enables an entity to exist in more than one form
C++ supports function overloading and operator overloading to implement polymorphism

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C++ Classes �&�Objects��

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Classes & Objects

Object-oriented programming (OOP)

Encapsulates data (attributes) and functions (behavior) into packages called classes.

So, Classes are user-defined (programmer-defined) types.

Data (data members)
Functions (member functions or methods)

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Classes in C++

A class definition begins with the keyword class.
The body of the class is contained within a set of braces, { } ; (notice the semi-colon).

class class_name

{

….

};

Class body (data member + methods)

Any valid identifier

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Classes in C++

Within the body, the keywords private: and public: specify the access level of the members of the class.

the default is private.

Usually, the data members of a class are declared in the private: section of the class and the member functions are in public: section.

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Classes in C++

class class_name

{

private:

…

public:

…

};

Public members or methods

private members or methods

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Classes in C++

Member access specifiers

public:

can be accessed outside the class directly.

The public stuff is the interface.

private:

Accessible only to member functions of class
Private members and methods are for internal use only.

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Class Example

This class example shows how we can encapsulate (gather) a circle information into one package (unit or class)

class Circle

{

private:

double radius;

public:

void setRadius(double r); double getDiameter();

double getArea();

double getCircumference();

};

No need for others classes to access 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)

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Creating an object of a Class

Declaring a variable of a class type creates an object. You can have many variables of the same type (class).

Once an object of a certain class is created, a new memory location is created for it to store its data members and code.

You can create many objects from a class type.

Ex) Circle c1,c2;

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Special Member Functions

Constructor:

Public function member
called when a new object is created (instantiated).
Initialize data members.
Same name as class
No return type
Several constructors

Function overloading

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Special Member Functions

class Circle

{

private:

double radius;

public:

Circle();

Circle(int r);

void setRadius(double r);

double getDiameter();

double getArea();

double getCircumference();

};

Constructor with no argument

Constructor with one argument

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Implementing class methods

Class implementation: writing the code of class methods.
There are two ways:

Member functions defined outside class

Using scope resolution operator (::)

Format for defining member functions

ReturnType ClassName::MemberFunctionName( ){

…

}

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Implementing class methods

Member functions defined inside class

Do not need scope resolution operator, class name;

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Accessing Class Members

Operators to access class members

Identical to those for structs
Dot member selection operator (.)

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Destructors

Destructors

Special member function
Same name as class

Preceded with tilde (~)

No arguments
No return value
Cannot be overloaded
Before system reclaims object’s memory

Reuse memory for new objects
Mainly used to de-allocate dynamic memory locations

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Structure vs class in C++�

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Members of a class

Members of a class are private by default

And

Members of a structure are public by default.

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// Program 1

class Test

{

int x; // x is private

};

int main()

{

Test t;

t.x = 20;

// compiler error because x is private

return 0;

}

struct Test

{

int x;

// x is public

};

int main()

{

Test t;

t.x = 20; // works fine because x is public

return 0;

}