Advanced-C++/C2/Polymorphism/English

Title of script: polymorphism in C++

Author: Ashwini Patil

Keywords: polymorphism, virtual members, Video tutorial.

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Polymorphism in C++.
Slide 2	In this tutorial we will learn, Polymorphism. Virtual members. We will do this with the help of examples.
Slide 3	To record this tutorial, I am using Ubuntu OS version 11.04 gcc and g++ compiler v. 4.6.1
Slide 4	Let us start with the introduction to polymorphism. Polymorphism is the ability of an entity to take different forms. It is the mechanism to use a function with same name in different ways.
Slide 5	Virtual function is the member function of a class. It can be overriden in its derived class. It is declared with virtual keyword. Virtual function call is resolved at run-time.
Open the file virtual.cpp Point the cursor to the file name	Let us see an example on virtual functions. In this program, We will calculate the area of a rectangle, parallelogram and traingle. Using virtual function. I have already typed the program on the editor. Lets go through it.
Highlight #include <iostream> using namespace std;	This is our header file as iostream. Here we are using std namespace.
Highlight class Parallelogram protected: int width, height, ar;	This is class parallelogram the base class. Then we have width, height and ar as variables.
Highlight public: void set_values (int a, int b)	set_values is the public function. We have passed two arguments as int a and int b.
Highlight virtual int area () { ar=width*height; cout<< "Area of parallelogram is "<< ar<<"\n"; }	Then we have virtual function area. Here we calculate the area of the parallelogram.
Highlight class Rectangle: public Parallelogram	Here Rectangle is the derived class.
Highlight int area () { ar=width * height; cout<< "Area of rectangle is "<<ar <<"\n"; }	In this we calculate the area of the rectangle.
Highlight class Triangle: public Parallelogram	Now we have triangle as derived class.
Highlight int area () { ar=width * height / 2; cout<< "Area of triangle is "<< ar<<"\n"; }	Here we calculate the area of the triangle.
Highlight int main()	This is our main function.
Highlight Parallelogram *parallel, p;	Then we create an object of class parallelogram.
Highlight *parallel, p;	*parallel is the pointer to class parallelogram. This is called as Base pointer. p is the object of class parallelogram. Pointer of base class can point to the object of the derived class.
Highlight Rectangle rect; Triangle trgl;	Rect is the object of class Rectangle. And trgl is the object of class Triangle.
Highlight parallel=&p; parallel->set_values(3,2);	Parallel is assigned to the address of p. Here we pass arguments as 3 and 2.
Highlight parallel->area();	Then we call function area.
Highlight parallel=&rect; parallel->set_values(4,5); parallel->area();	Parallel is assigned to the address of rect We pass arguments as 4 and 5. Again we call the function area.
Highlight parallel=&trgl; parallel->set_values(6,5); parallel->area();	Now, Parallel is assigned to the address of trgl We pass arguments as 6 and 5. Then we call area function.
Highlight return 0;	This is the return statement
Click on save	Now Click on Save
	Let us execute
Open the terminal Ctrl, Alt and T keys simultaneously	Please open the terminal by pressing Ctrl, Alt and T keys simultaneously
Type g++ virtual.cpp -o virtual To execute Type ./virtual	To compile the program type g++ virtual.cpp -o virtual To execute Type ./virtual
Highlight Output	Here we see, Area of parallelogram is 6 Area of rectangle is 20 Area of triangle is 15
Switch back to the slides	This brings us to the end of this tutorial. Let us come back to the slides.
Slide 7 Summary	In this tutorial, we have seen, Polymorphism. Virtual function.
Slide 6 Assignment	As an assignment Calculate the perimeter of rectangle, square and triangle. Create perimeter as a virtual function.
Slide 8 About the Spoken Tutorial Project	Watch the video available at the link shown It summarizes the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Slide 9 Spoken Tutorial Workshops	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 Indiaabout:startpage 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