View source for Advanced-C++/C2/Polymorphism/English-timed

 
{| border=1
|| '''Time'''
|| '''Narration'''

|-
|  00:02
|   Welcome to the '''spoken tutorial''' on '''Polymorphism'''in '''C++'''.

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|  00:07
|  In this tutorial, we will learn:

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|  00:10
|* '''Polymorphism'''

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|  00:11
|* '''Virtual Function.'''

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| 00:13 
| We will do this through an example.

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|  00:16
|  To record this tutorial, I am using:
* '''Ubuntu OS '''version '''11.10'''
* '''g++ compiler '''version 4.6.1'''

|-
|   00:27
|  Let us start with the introduction to '''polymorphism.'''

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|  00:31
| '''Polymorphism '''is the ability to take different forms.

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|00:36  
| It is the mechanism to use a '''function''' with same name in different ways.

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|  00:42
|  Let us see '''virtual functions'''.

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|  00:45
| '''Virtual''' function is the member function of a '''class'''. 

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|  00:49
| It can be overridden in its '''derived class.'''

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|  00:53
| It is declared with '''virtual keyword'''. 

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|  00:57
| '''Virtual function''' call is resolved at '''run-time.'''

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|  01:01
|   Now let us see an example on '''virtual functions.'''

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|  01:06
| I have already written the '''code'''.

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|  01:08
| Let us go through it.

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|  01:10
| Note that our file name is '''virtual.cpp'''.

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|  01:15
| In this program:

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|  01:16
| We will calculate the area of a rectangle, parallelogram and triangle.

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|  01:22
|   This is our '''header file''' as '''iostream.'''

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|  01:25
| Here we are using '''std namespace.'''

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|   01:29
|  Then we have a '''class parallelogram''' 

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|  01:33
| This is the '''base class.'''

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|  01:35
| In this, we have declared''' integer variables''' as '''width,height''' and '''ar.'''

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|  01:42
| These are declared '''protected.'''

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|  01:45
|   Then we have function '''set_values()''', declared as '''public.'''

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|  01:50
| Here we have passed two '''arguments''' as '''a ''' and''' b.'''

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|  01:55
| Then we access the '''protected''' members using the '''public members'''.

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|   02:00
| This is our '''virtual function "area".'''

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|  02:04
| Here we calculate the area of parallelogram.

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|   02:07
|   Then we have '''class''' '''Rectangle''' as a '''derived class.'''

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|  02:12
| It inherits the properties of '''base class''' '''parallelogram'''.

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|   02:17
|  Here we '''override''' the function '''area'''.

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|  02:21
| Then we calculate the area of the rectangle.

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|  02:23
| And '''print''' the '''value'''.

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|   02:25
|  Here we have another derived '''class''' as '''triangle'''.

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|  02:29
| This also inherits the properties of the '''base class''' '''parallelogram'''.

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|  02:35
| Here again we '''override''' the function '''area'''.
 
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|   02:39
|   Then we calculate the area of the triangle.

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|  02:41
| And '''print''' the '''value'''.

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|  02:43
| This is our '''main()''' function.

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|  02:46
|  Here we create an '''object'''of '''class parallelogram''' as '''p.'''

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|  02:52
| We can see here '''pointer parallel.'''

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|  02:56
|  This is the '''pointer''' of '''class''' '''parallelogram.'''

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|  03:00
| This is called as '''Base pointer.'''

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|  03:03
| '''Pointer''' of '''base class''' can point to the '''object''' of the '''derived class'''.

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|  03:08
| Here we create objects of class''' Rectangle and Triangle.'''

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|   03:14 
|  Here, '''Parallel''' is assigned to the address of '''p.'''

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|  03:18
| Then we pass''' arguments '''as''' 3 '''and''' 2.'''

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|  03:23
| Then we call function '''area().'''

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| 03:26
|   Here, '''Parallel''' is assigned to the address of '''rect'''.

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|  03:30
| '''rect''' is the '''object''' of '''class''' '''Rectangle.'''

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|  03:33
| Again we pass '''arguments '''as''' 4 '''and''' 5.'''

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|  03:37
| And we call the function '''area().'''

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|   03:40
|  And, at last we assign '''Parallel''' to the address of '''Triangle '''

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|  03:45
| '''trgl.'''

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|  03:47
| This is the object of '''class Triangle.'''

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|  03:51
| Here, we pass '''arguments '''as''' 6 '''and''' 5'''

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|  03:54
| and call''' function area().'''

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| 03:56
| And this is our '''return''' statement.

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| 03:59
| Now,  let us '''execute''' the program.

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|   04:02
|  Open the '''terminal window''' by pressing '''Ctrl, Alt''' and '''T '''keys simultaneously on your keyboard.

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|   04:09
|  To compile, type: 

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|  04:10
| '''g++ space virtual.cpp space -o space vir''' press '''Enter'''.

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|  04:20
| Type: '''./vir ''' press '''Enter'''.

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| 04:24
| You can see that the '''output''' is displayed as:

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|  04:27
| '''Area of parallelogram is 6 '''

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|  04:29
| '''Area of rectangle is 20 '''

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|  04:31
| and '''Area of triangle is 15'''.

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| 04:34
|   Come back to  our '''slides'''.

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|  04:36
| Let us summarize.

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|  04:37
|  In this tutorial, we  learnt:

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|  04:39
|* '''Polymorphism'''

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|  04:41
|* Virtual function, example '''Virtual int area()'''.

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|  04:45
|  As an assignment: 

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|  04:46
|* Calculate the perimeter of rectangle, square and triangle.

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|  04:50
|* Create perimeter as a '''Virtual function.'''

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|  04:54
| Watch the video available at the link shown  below.

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|  04:57
| It summarizes the Spoken-Tutorial project. 

|-
|  05:00
| If you do not have good bandwidth, you can download and watch it.

|-
| 05:04
|  The Spoken Tutorial Project team: 

|-
|  05:06
| Conducts workshops using spoken tutorials. 

|-
|  05:09
| Gives certificates to those who pass an Online test. 

|-
|  05:14
| For more details, please write to, contact@spoken-tutorial.org

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|  05:21
| Spoken-Tutorial Project is a part of the "Talk to a Teacher" project.

|-
| 05:25 
| It is supported by the National Mission on Education through ICT, MHRD, Government of India.

|-
|  05:32
| More information on this mission is available at link shown below : [http://spoken-tutorial.org/NMEICT-Intro]

|-
|05:37
|This is Ashwini Patil from IIT Bombay, signing off.
Thank You for joining. 

|}