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 through an example.
Slide 3	To record this tutorial, I am using Ubuntu OS version 11.10 gcc and g++ compiler v. 4.6.1
Slide 4	Let us start with the introduction to polymorphism. Polymorphism is the ability to take different forms. It is the mechanism to use a function with same name in different ways.
Slide 5	Let us see virtual functions. 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	Now let us see an example on virtual functions. I have already written the code. Let us go through it. Note that our filename is virtual.cpp In this program: We will calculate the area of a rectangle, parallelogram and traingle.
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;	Then we have a class parallelogram This is the base class. In this we have declared integer variables as width, height and ar. These are declared protected.
Highlight public: void set_values (int a, int b)	Then we have function set_values declared as public. Here we have passed two arguments as a and b. Then we access the protected members using the public members.
Highlight virtual int area () { ar=width*height; cout<< "Area of parallelogram is "<< ar<<"\n"; }	This is our virtual function area. Here we calculate the area of parallelogram.
Highlight class Rectangle: public Parallelogram	Then we have class Rectangle as derived class. It inherits the properties of base class parallelogram.
Highlight int area () { ar=width * height; cout<< "Area of rectangle is "<<ar <<"\n"; }	Here we override the function area. Then we calculate the area of the rectangle. And print the value.
Highlight class Triangle: public Parallelogram	Here we have another derived class as triangle. This also inherits properties of the base class parallelogram. Here again we override the function area.
Highlight int area () { ar=width * height / 2; cout<< "Area of triangle is "<< ar<<"\n"; }	Then we calculate the area of the triangle. And print the value.
Highlight int main()	This is our main function.
Highlight Parallelogram *parallel, p;	Here we create an object of class parallelogram as p. We can see here pointer parallel.
Highlight *parallel, p;	This is the pointer of class parallelogram. This is called as Base pointer. Pointer of base class can point to the object of the derived class.
Highlight Rectangle rect; Triangle trgl;	Here we create objects of class Rectangle and Triangle.
Highlight parallel=&p; parallel->set_values(3,2);	Here, Parallel is assigned to the address of p. Then 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();	Here, Parallel is assigned to the address of rect rect is the object of class Rectangle. Again we pass arguments as 4 and 5. And we call the function area.
Highlight parallel=&trgl; parallel->set_values(6,5); parallel->area();	And at last we assign Parallel is assigned to the address of Triangle trgl. This is the object of class Triangle. Here we pass arguments as 6 and 5. And call function area.
Highlight return 0;	This is the return statement
	Let us execute the program
Open the terminal Ctrl, Alt and T keys simultaneously	Please open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
Type g++ virtual.cpp -o vir To execute Type ./vir	To compile the program type: g++ virtual.cpp -o vir Press Enter Type: ./vir Press Enter
Highlight Output	We can see that, The output is displayed as: Area of parallelogram is 6 Area of rectangle is 20 Area of triangle is 15
Switch back to the slides	Come back to the slides. Let us summarize.
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