Advanced-C++/C2/Constructor-And-Destructor/English

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Title of script: Constructors and Destructors

Author: Ashwini R. Patil

Keywords: Constructors, Destructors, Video tutorial


Visual Cue
Narration
SPreferable to have the title of the slide like Introduction/prerequisite etc...lide 1 Welcome to the spoken tutorial on Constructors and Destructors in C++.
Slide 2


In this tutorial we will learn about,

Constructors.

Types of constructors

Destructors.

We will do this with the help of example.

Slide 3


To record this tutorial, I am using

Ubuntu Operating System version 11.10,

g++ Compiler version 4.6.1.

Slide 4 Let us start with the introduction to Constructors and Destructors.

A constructor is a member function.

It has the same name as the class name.

Constructors cannot return values.

Constructor is automatically called when an object is created.

Types of Constructors are:

Parameterized Constructors.

Copy Constructors.

Default Constructors.

We will discuss about them in another tutorial.No details about destructors. Pls change the opening statement or provide an additional slide for destructors.

Let us move on to Destructors

Destructors are used to deallocate memory.

They are called when an object is destroyed.

A destructor takes no arguments and has no return types.

Let us look at an example of Constructors,

I have already typed the code on the editor,

So i will open it.

Point the cursor

constructor.cpp

I have saved the file with the name constructor.cpp

Let me explain the code now.

Highlight

#include <iostream>

This is our header file as iostream.
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using namespace std;

Here is the std namespace.
Highlight

class Addition

Here we have defined a class Addition.



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int a, b ;

a and b are the integer variables.
Highlight

public

Public is the access specifier.

It allows the data to be accessible by the other parts of our program.

Highlight

Addition(int, int)

Addition is the construtor here.

A constructor has the same name as the class name.

We have passed two arguements here.

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int add( )

Then we have defined a function add.



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return(a + b);

It returns sum of a and b.
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Addition :: Addition (int a, int b)

Here, we specify that function Addition is not a global function.

It is a member function of the class Addition.

Here we have passed two arguments.

int x and c-c++-constructors-&-destructors-c3-eng.odtint y.

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a = x;

b = y;

Now the value of x will be stored in variable a.

And the value of y will be stored in variable b.

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int main()

This is our main function.
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Addition obj (3, 4);

obj is the object of class Addition.

Here we pass two values as 3 and 4.

3 will be stored in x and 4 will be stored in y.

Which means a's value will be 3 and b's vaue will be 4.

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cout << “Addition of a and b is ” <<obj.add() <<“\n”

Then we print the result.

Here we call the function add through the object obj.

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return 0;

This is our return statement.
Click on save Now click on Save.
Let us execute the program.
Open the terminal

Ctrl, Alt and T keys simultaneously

Open the terminal by pressing Ctrl, Alt and T keys simultaneously.
Type

g++ constructor.cpp -o cons

To execute

Type

./cons

To compile the program type,

g++ constructor.cpp -o cons

To execute

Type

./cons

Highlight

Output

Here the output is displayed as

Sum is 7.

And

Memory Deallocation

On the editor Now let us see an example on Default constructors.

Come back ot our program.

I have already typed the code.

Note that our filename is default.cpp

Default Constructor Note that our filename is default.cpp.

If a constructor is not declared in the class,

Then the compiler assumes a default constructor for the class.

Let me explain the code.

This is our header file as iostream.

Here we have used std namespace.
Point cursor to filename


Highlight

class Subtraction


Then we have class Subtraction.

Then we a and b declared as public.

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int sub(int a, int b)

return (a-b);

Here we have sub function.

We have passed two arguments int a and int b.

This returns the subtraction of two numbers a and b.

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Subtraction ();


This is the defalut constructor.

Here we access the default constructor using the scope resolution operator.

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int main()

int x;

This is our main function.

In this we have defined a variable x.

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Subtraction s;

Here we create an object s of class subtraction.
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x=s.sub(8,4);

Then we call the function sub using the object s.

And pass two arguments as 8 and 4.

Then the result is stored in variable x.

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cout <<"Difference is "<<x<<"\n";

return 0;

And here we print the difference.

This is our return statement.

On the terminal Let us execute the program.

Come back to our terminal.

Type

g++ default.cpp -o def

Type

./def

Type

g++ default.cpp -o def

Type

./def

Highlight

Output

The output is return as

Difference is 4

Come back to our program.

Here you can see that we have passed the arguments within the function.

And in our previous program we have passed the arguments within the object
And here we have passed the arguments using the object.



Now let us go back to our program.
Slide 6 Let us summarize,

In this tutorial we learned,

Constructors.

eg. Addition

Parameterized Constructor.

eg. Addition obj (3, 4);

Destructors

eg. ~Addition

Default Constructor.

eg. Subtraction

Slide 7 As an assignment,

Create a class named Division.

Create a constructor for the class

Create a function divide which divides two given numbers.

Slide 8

About the Spoken Tutorial Project

Watch the video avail able at the link shown .

It summarises the Spoken Tutorial project.

If you do not have good bandwidth, you can download and watch it.

Slide 9

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The Spoken Tutorial Project Team,

Conducts workshops using spoken tutorials .

Gives certificates to those who pass an online test .

For more details, please write to,

contact@spoken-tutorial.org

Slide Number 10


Acknowledgement

Spoken Tutorial Project is a part of the Talk to a Teacher project.

It is supported by the National Mission on Education through ICT, MHRD, Government of India.

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro.

This is Ashwini Patil from IIT Bombay signing off

Thank You for joining.

Contributors and Content Editors

Ashwini

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