View source for Advanced-C++/C2/Inheritance/English

'''Title of script''': Constructors and Destructors

'''Author: '''Ashwini R. Patil

'''Keywords: Constructors, Destructors, Video tutorial'''



{| style="border-spacing:0;"
! <center>Visual Cue</center>
! <center>Narration</center>

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 1
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on Constructors and Destructors in C++.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 2



| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn about,

'''Constructors.'''

'''Destructors.'''

We will do this with the help of example.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 3 



| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| To record this tutorial, I am using

'''Ubuntu Operating System''' version 11.04,

'''g++''' '''Compiler''' version 4.6.1.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 4
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''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'''.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let us look at an example of '''Constructors''',

I have already typed the code on the editor,

So i will open it.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Point the cursor

'''constructor.cpp'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| I have saved the file with the name '''constructor.cpp'''

Let me explain the code now.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''<nowiki>#include <iostream></nowiki>'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is our '''header file as iostream.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''using namespace std;'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here is the '''std''' namespace.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''class Addition'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we have defined a class '''Addition.'''




|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''int a, b ;'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''a''' and '''b''' are the integer variables.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''public'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''Public''' is the '''access specifier.'''

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

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''Addition(int, int)'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''Addition''' is the construtor here.

A '''constructor''' has the same name as the class name.

We have passed two arguements here.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''int add( )'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Then we have defined a function '''add.'''




|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''return(a + b);'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| It returns sum of a and b. 

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''Addition :: Addition (int a, int b)'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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 '''int y.''' 

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''a = x;'''

'''b = y;'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now the value of '''x''' will be stored in variable '''a'''.

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

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''int main()'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is our '''main function.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''Addition obj (3, 4);'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''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.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''<nowiki>cout << “Addition of a and b is ” <<obj.add() <<“\n”</nowiki>'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Then we print the result. 

Here we call the function '''add '''through''' '''the object''' obj'''.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''return 0;'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is our '''return''' statement.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Click on save
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now click on '''Save'''.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let us execute the program.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Open the terminal

'''Ctrl, Alt and T''' keys simultaneously
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Open the terminal by pressing '''Ctrl, Alt and T''' keys simultaneously.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type 

'''g++ constructor.cpp -o cons'''

To execute

Type

'''./cons'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| To compile the program type,

'''g++ constructor.cpp -o cons'''

To execute

Type

'''./cons'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''Output'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here the output is displayed as 

'''Sum is 7.'''

'''And'''

'''Memory Deallocation'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| On the editor
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Go to '''File''' menu

Click on '''Save as''' option
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| If a constructor is not declared in the class then the compiler assumes a default constructor for the class.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is our '''header file as iostream.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here is the '''std''' namespace.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type:

'''Addition::~Addition();'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here type '''Addition::~Addition()'''

Opening curly bracket '''{ '''

then type '''<nowiki>cout << "Memory Deallocation\n"; </nowiki>'''

and closing surly bracket '''}'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| On the terminal
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let us execute.

Come back to the terminal.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type 

'''g++ destructor.cpp -o dest'''

Type

'''./dest'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Compile and execute as before.

'''g++ destructor.cpp -o dest, '''

and press''' Enter.'''

To execute,

Type,

'''./dest'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''output'''
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here the output is displayed as, 

'''Addition of a and b is 7.'''

'''Memory Deallocation.'''

This brings us to the end of this tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 6
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let us summarize,

In this tutorial we learned,

'''Constructors'''

eg. '''Addition'''

'''Destructors'''

eg. '''~Addition'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 7
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| As an assignment,

Write a program to calculate the area of a triangle using constructor.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 8

About the Spoken Tutorial Project
| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 9

Spoken Tutorial Workshops



| style="background-color:transparent;border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide Number 10


Acknowledgement
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| 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.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is Ashwini Patil from IIT Bombay signing off

Thank You for joining. 

|}