Advanced-C++/C2/Abstract-Class/English

Title of script: Abstract class and pure virtual function in C++

Author: Ashwini Patil

Keywords: abstract class, pure virtual function, Video tutorial.

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on abstract class and pure virtual function in C++.
Slide 2	In this tutorial we will learn, Abstract Classes Pure virtual function We will do this with the help of an example.
Slide 3	To record this tutorial, I am using Ubuntu OS version 11.04 g++ compiler v. 4.6.1
Slide 4	Abstract class is used as a base class. It contains one pure virtual function. We cannot create an instance of abstract class.
Slide 5	A pure virtual function is a function with no body. It is not defined in the base class. It is declared as follows: virtual void virtualfunname()=0; A derived class must override the function. Otherwise will give an error. It is upto a derived class to implement the function.
Open abstract.cpp	Let us look at an example This example involves addition and subtraction of two numbers. I have already typed the code on the editor.
Point the cursor abstract.cpp	I have saved the file with the name abstract.cpp Let me explain the code now.
Highlight #include<iostream>	This is our header file iostream.
Highlight using namespace std;	This is the using statement.
Highlight class abstractinterface	This is declaration for a class named abstractinterface.
Highlight public:	Then we have public specifier.
Highlight virtual void numbers()=0;	In this we have pure virtual function as numbers initialized to 0. This is the declaration for virtual function. It is defined when it is used.
Highlight void input(); int a, b;	Then a non-virtual function input is declared. And we have a and b as integer variables.
Highlight void abstractinterface::input() { cout<< "Enter the numbers\n"; cin>>a>>b; }	In function input we take the value of a and b as user input.
Highlight class add : public abstractinterface	Now we create a derived class as add. It inherits the base class abstractinterface.
Highlight public: void numbers() { int sum; sum=a+b; cout<<"sum is "<<sum<<"\n"; }	Now we have function numbers In this we add the values of a and b. And print the sum.
Highlight class sub : public abstractinterface { public:	Here we create another derived class sub. This also inherits the base class abstractinterface.
Highlight void numbers() { int diff; diff=a-b; cout<<"diff is "<<diff<<"\n"; }	Then we have numbers function. This calculates the difference of two numbers. And prints the result.
Highlight int main()	This is our main function.
Highlight add obj1; obj1.input(); obj1.numbers();	Here, obj1 is the object of class add. Then we call function input and numbers using object obj1.
Highlight sub obj2; obj2.input(); obj2.numbers();	Now we create an object obj2 of class sub. And we call the input and numbers function using object obj2.
Highlight return 0;	This is the return statement.
Click on Save	Now Click on Save
	Let us execute
Open the terminal Ctrl, Alt and Tkeys simultaneously	Open the terminal by pressing Ctrl, Alt and T keys simultaneously
Type g++ abstract.cpp -o abs To execute Type ./abs	To compile the program type g++ abstract.cpp -o abs To execute type ./abs
Highlight Output	It is displayed as Enter the numbers I will enter as 12 4 The output is displayed as 16 Enter the numbers I will enter as 9 3 The output is displayed as 6
	This brings us to the end of this tutorial. Let us move back to slides.
Slide 6 Summary	In this tutorial we have seen Abstract class eg. class abstractinterface Pure virtual function eg. virtual void numbers()=0;
Slide 7 Assignment	As an assignment Create an abstract class student. Create a pure virtual function as Info Accept the name and roll no of the student in the function. Create two derived class marks and sports. In marks accept marks of three subjects. In sports enter marks scored in sports. Calculate the total marks. Then create another derived class result. In this display the name, roll-no, total marks of the student.
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 India 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, Nancyvarkey