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<h3 class="pb-3 pt-3">Objects and Classes</h3>

<p>In this tutorial we are going to learn about classes and object in C++

with the help of some examples.</p>

<p>In this course, till now we have created functions to do a specific task or

related task. we also need to create different variables separately to

access the function</p>

<p>However, in C++ we don’t need to create functions and variables (or

data) separately, we can wrap them into single a entities called object,

which contains members to perform tasks and variables to access

them. This unique feature pioneered a new kind of computer

programming called <strong>object oriented programming</strong>.

</p>

<p>This provided more security and neat packaging to code. Also they

provide real-life touch to programming. we will learn more about it

later in this chapter.</p>

<hr/>

<h4 class="pt-3 pb-3">Classes</h4>

<p>a class is a blueprint of objects</p>

<p>consider an example of bicycles, each and every bicycle in this world

have same characteristics like two wheels , paddle , handle etc. And

also have same functions like moving, running etc. Thus a bicycle is an

object of class of bicycles, which defines its characteristics and

functions.

</p>

<p>Hence class of bicycle act as blueprint for bicycles.</p>

<hr/>

<h4 class="pt-3 pb-3">Creating a class in C++</h4>

<p>Lets see how to create classes in c++</p>

<p>A class is defined in C++ using keyword <strong>class</strong> followed by the name of

the class.<br>

The body of the class is defined inside the curly brackets and

terminated by a semicolon at the end.</p>

<pre>class className {

// some data

// some functions

};

</pre>

<p>Lets understand this with example of <strong>class</strong> of students. Students can

have <strong>data</strong> like name, roll_no., grade etc. And can do <strong>functions</strong> like

taking exams, submit fees, ask doubts etc.

</p>

<pre>class student{

//data

char name[20];

int roll_no.;

char grade

//functions

Take_exam();

Submit_fees;

Ask_doubts();

};</pre>

<p>From above example, it may be seen that class contains <strong>data</strong> in form of

variables( eg. <strong>Name</strong>, <strong>roll_no.</strong> and <strong>grade</strong>),known as data members</p>

<p>And functions(eg. <strong>Take_exam()</strong>, <strong>Submit_fees()</strong> and <strong>Ask_doubts()</strong>),

known as <strong>member functions</strong>

</p>

<p>Let’s take one more better understanding .

</p>

<pre>class Room {

public:

double length;

double breadth;

double height;

double calculateArea(){

return length * breadth;

}

double calculateVolume(){

return length * breadth * height;

}

};</pre>

<p>Here, in the above example, <strong>length, breadth</strong> and <strong>height</strong> are <strong>data

members</strong>. And <strong>calculateArea()</strong> and <strong>calculateVolume()</strong> are <strong>member

functions</strong> .</p>

<hr/>

<h4 class="pt-3 pb-3">Objects</h4>

<p>Again consider the example of class of students, each and every student

of this world would belong to this class, as they have same

characteristics and functions.</p>

<p>Thus we can say that objects are instances of their class.</p>

<hr/>

<h4 class="pt-3 pb-3">Creating objects in C++</h4>

<p>When we define a class, only the blue print of object is defined, hence

no memory allocation takes place. The memory allocation takes place

when we create object of that particular class.</p>

<p>Syntax of creating object is given below.</p>

<p>We can create object of class <strong>students</strong> as follows:</p>

<pre>class students{

public:

//data

char name[20];

int roll on.;

char grade

//functions

Take_exam();

Submit_fees;

Ask_doubts();

};

int main(){

students s1,s2,s3;

... .. ...

return 0;

}</pre>

<p>In above example you can see the piece of code <strong>students s1,s2,s3;</strong></p>

<p>It is nothing but creation of three objects <strong>s1,s2 </strong>and <strong>s3</strong> of class<strong> students</strong>.

you can create as many objects as you wish.

</p>

<hr/>

<h4 class="pt-3 pb-3">Accessing member functions of a class</h4>

<p>you can access member functions of a class after creating its object.<br>

The syntax of code to access class is given below.

</p>

<pre><object_variable_name>.<member_function>;

</pre>

<p>For example, to access member function <strong>Take_exam()</strong>of class

<strong>students</strong>, we can write

</p>

<p>you may have noticed the <strong>dot(.)</strong> between <strong>s1</strong> and <strong>Take_exam()</strong>. This dot

is called <strong>access operator</strong>. We use this operator along with object to

access member functions</p>

<p>Similary, we can access data members</p>

<pre>s1.roll_no.=55;

</pre>

<hr/>

<h4 class="pt-3 pb-3">Access Specifiers in C++</h4>

<p>Access specifiers are used to implement an important feature of

Object-Oriented Programming known as <strong>Data hiding</strong>.

</p>

<p>Again consider the example of <strong>students</strong>, from the previous topic it is

clear that any function can access and modify the data members and

member functions of a class, which is a serious drawback regarding

<strong>data security</strong>. Hence, C++ provides various access specifiers to ensure

data security. These are

</p>

<ol>

<li><strong>Private</strong> access specifier</li>

<li><strong>Public</strong> access specifier</li>

<li><strong>Protected</strong> access specifier</li>

</ol>

<p>for now we will only discuss first two</p>

<ol>

<li><strong>Private</strong> access specifier : The class members (data members and

functions) declared as private can be accessed only by the functions

inside the class. They are not allowed to be accessed directly by any

object or function outside the class.<br><br>

Suppose, we want to hide the member functions of class students.

We will do the following

<pre>class students{

private:

//data

char name[20];

int roll on.;

char grade

//functions

Take_exam();

Submit_fees;

Ask_doubts();

};</pre>

This will hide all class members from outside functions, so they can’t

access them easily.

</li><br>

<li><strong>Public</strong> access specifier: All the class members declared under public

will be available to everyone. The data members and member

functions declared public can be accessed by other classes too. The

public members of a class can be accessed from anywhere in the

program using the direct member access operator (.) with the object

of that class.

<pre>class students{

public:

//data

char name[20];

int roll on.;

char grade

//functions

Take_exam();

Submit_fees;

Ask_doubts();

};</pre>

Now each class member can be easily accessed by any function.</li>

</ol>

<p><strong>Note:

</strong>by default each and every member of a class is

<strong>private</strong>. So <strong>private</strong> is the default access specifier of a class.</p>

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