Difference between revisions of "Advanced-C++/C2/Classes-And-Objects/English"

Classes.

Objects.

Encapsulation. and

Data abstraction.

We will do this with the help of an example.

Ubuntu OS version 11.10

g++ compiler version 4.6.1

Class is created using a keyword class

It holds data and functions.

Class links the code and data.

The data and functions of the class are called as members of the class.

Objects are variables.

They are the copy of a class.

Each of them has properties and behavior.

Properties are defined through data elements. And

Behavior is defined through member functions called methods.

class class-name

{

public:

(public member functions)

};

Here, class is a keyword used to define a class.

Class-name is the name of the class.

Public, private and protected are the access specifier.

And here we have defined the Data members and the member functions

As public, private and protected.

This is how we close the class.

I have already typed the code on the editor.

I will open it.

class-obj.cpp

In this example we will calculate the area of a square using class.

Let me explain the code now.

#include<iostream>

using namespace std;

class square

int x;

Here I have not declared any access specifier. So by default it is private. Hence variable x is a private member of class square.

public

Function area is a public function.

And this is how we close the class.

Now let us move back to our slides to know more about the access specifiers.

The public specifier allows the data to be accessed outside the class.

A public member can be used anywhere in the program.

The members declared as private cannot be used or accessed outside the class.

Private members can be used only by the members of the class.

Protected members cannot be accessed from outside the class.

They can be accessed by a derived class.

Let us move back to our program.

The scope resolution operator and the function name.

We must use this operator.

It specifies that function area is not a global function.

It is a member function of class square.

Now let us switch back to the slides to know more about the scope resolution operator.

To access the variable or function with the same name we use the scope resolution operator ::.

Suppose the local variable and the global variable have same name.

The local variable gets the priority.

We can access the global variable using scope resolution :: operator.

{

return (x*x);

}

Here x is a private member.

To access the private parameter we used the public member a.

private members are always hidden.

int main()

square sqr;

This is how we create an object

class-name followed by the object-name

cout <<"Area of the square is " <<sqr.area() << “\n”;

Then we pass an argument as 4.

we set the value of x as 4.

return 0;

Ctrl, Alt and Tkeys simultaneously

g++ class-obj.cpp -o class

To execute

Type

./class

g++ space class-obj.cpp space -o space class

Press Enter

Type

./class

Press Enter

Output

Area of the square: 16

class square

{

int x;

public:

int area(int);

};

What does Encapsulation mean.

What is Data abstraction..

The data and functions combined together in a class.

Class is a single unit.

In which the data and the function using them is grouped.

This mechanism is called as Encapsulation.

Then we have seen class with the private and public members.

The private data is hidden.

It cannot be accessed outside the class.

This mechanism is called as Data abstraction.

The interface is seen but the implementation is hidden.

Let us move back to our slides.

Summary

In this tutorial we have learnt,

Encapsulation

Data Abstraction

Private members

int x;

Public functions

int area(int);

Classes

class square

To create object-name

square sqr;

To call a function using object

sqr.area(); 

Assignment

write a program to find the perimeter of a given circle.

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