Advanced-C++/C2/Polymorphism/English-timed

Time	Narration
00:02	Welcome to the spoken tutorial on Polymorphismin C++.
00:07	In this tutorial, we will learn:
00:10	* Polymorphism Virtual Function.
00:13	We will do this through an example.
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 an introduction to polymorphism.
00:31	Polymorphism is the ability to take different forms.
00:36	It is the mechanism to use a function with same name in different ways.
00:42	Let us see virtual functions.
00:45	Virtual function is the member function of a class.
00:49	It can be overridden in its derived class.
00:53	It is declared with virtual keyword.
00:57	Virtual function call is resolved at run-time.
01:01	Now, let us see an example on virtual functions.
01:06	I have already written the code.
01:08	Let us go through it.
01:10	Note that our file name is virtual.cpp.
01:15	In this program,we will calculate the area of a rectangle, parallelogram and triangle.
01:22	This is our header file as iostream.
01:25	Here we are using the std namespace.
01:29	Then, we have a class Parallelogram.
01:33	This is the base class.
01:35	In this, we have declared integer variables as width, height and ar.
01:42	These are declared protected.
01:45	Then we have function set_values(), declared as public.
01:50	Here, we have passed two arguments as a and b.
01:55	Then we access the protected members using the public members.
02:00	This is our virtual function area().
02:04	Here we calculate the area of parallelogram.
02:07	Then we have class Rectangle as a derived class.
02:12	It inherits the properties of base class Parallelogram.
02:17	Here we override the function area().
02:21	Then we calculate the area of the rectangle.
02:23	And print the value.
02:25	Here we have another derived class as triangle.
02:29	This also inherits the properties of the base class Parallelogram.
02:35	Here again we override the function area().
02:39	Then we calculate the area of the triangle
02:41	and print the value.
02:43	This is our main() function.
02:46	Here we create an objectof class Parallelogram as p.
02:52	We can see here pointer parallel.
02:56	This is the pointer of class parallelogram.
03:00	This is called as Base pointer.
03:03	Pointer of base class can point to the object of the derived class.
03:08	Here we create objects of class Rectangle and Triangle.
03:14	Here, parallel is assigned to the address of p.
03:18	Then we pass arguments as 3 and 2.
03:23	Then we call the function area().
03:26	Here, parallel is assigned to the address of rect.
03:30	rect is the object of class Rectangle.
03:33	Again we pass arguments as 4 and 5.
03:37	And we call the function area().
03:40	And, at last we assign parallel to the address of Triangle
03:45	trgl.
03:47	This is the object of class Triangle.
03:51	Here, we pass arguments as 6 and 5
03:54	and call function area().
03:56	And this is our return statement.
03:59	Now, let us execute the program.
04:02	Open the terminal window by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
04:09	To compile, type:
04:10	g++ space virtual.cpp space -o space vir press Enter.
04:20	Type: ./vir press Enter.
04:24	You can see that the output is displayed as:
04:27	Area of parallelogram is 6
04:29	Area of rectangle is 20
04:31	and Area of triangle is 15.
04:34	Come back to our slides.
04:36	Let us summarize.In this tutorial, we learnt:
04:39	* Polymorphism
04:41	* Virtual function, example Virtual int area().
04:45	As an assignment: Calculate the perimeter of rectangle, square and triangle.
04:50	* Create perimeter as a Virtual function.
04:54	Watch the video available at the link shown below.
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05:37	This is Ashwini Patil from IIT Bombay, signing off.Thank You for joining.

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