C-and-C++/C2/Scope-Of-Variables/English

Title of script: Scope of variables

Author: Ashwini R. Patil

Keywords: Scope of variables, global variable, local variable, Video tutorial

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Scope of variables in C and C++.
Slide 2	In this tutorial we will learn, What is the Scope of variables. What is a Global variable. What is a Local variable. Few examples. We will also see some common errors and their solutions.
Slide 3	To record this tutorial, I am using Ubuntu Operating System version 11.04, gcc and g++ Compiler version 4.6.1
Slide 4	Let us start with the introduction to the scope of variables. It is the region of code within which the variable can be accessed. Depending on its type and place of declaration it is divided into two catagories: Global Variable. And Local Variable.
Type: #include<stdio.h>	Now we will see an example. I have already typed the program on the editor, Let me open it.
Point the cursor scope.c	Note that our filename is scope.c. Let me explain the code now.
Highlight #include <stdio.h>	This is our header file.
Highlight int a=5; int b=2;	Here we have declared two global variables a and b. And we have initialized them by assigning values as 5 and 2. A global variable is available to all functions in your program. These are declared outside any functions above main() funtion. These have a Global scope.
Highlight void add()	Here we have declared a function add without arguments.
Highlight int sum; sum = a+b;	Here sum is a local variable. It is declared inside the function add. A local variable is available only to the function inside which it is declared. These variables are declared inside a block. These have local scope. The sum of a and b will be stored in the variable sum.
Highlight printf("Sum is %d\n",c);	Here we print the sum.
Highlight int main()	This is our main function.
Highlight add();	The add function is called and then executed.
Highlight return 0;	And this is our return statement.
Click on save	Now Click on save.
	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 gcc scope.c -o sco To execute Type ./sco	To compile type, gcc space scope.c space -o space sco And press Enter To execute Type ./sco press Enter
Highlight Output	The output is displayed as Sum of a and b is 7
On the editor	NOW LET US SEE HOW TO EXECUTE THE SAME PROGRAM IN C++ Come back to our program
Go to File menu Click on Save as option Type .cpp	First press shfit+ctrl and s keys simultaneously on your keyboard. Now Save the file with an extension. .cpp and click on SAVE
Highlight header file	Let us change the header file as iostream.
Type using namespace std;	Now include the using statement. Click on Save.
	The declaration of global variable and local variable is same in C++. So no need to change anything.
Type cout <<	Now replace the printf statement with the cout statement
Delete %d\n	Delete the format specifier and '\n' Now delete the comma.
Type <<	Type two opening angle brackets.Delete the closing bracket. Again type two opening angle brackets and within the double quotes type backslash n. Now click on Save. Let us execute the program.
On the terminal	Come back to the terminal.
Type g++ scope.cpp -o sco1	To compile Type, g++ space scope.cpp space -o space sco1 Here we have sco1 because we don't want to overwrite the output parameter sco for the file scope.c Now press Enter.
Type ./sco1	To execute, Type, ./sco1 And press Enter.
Highlight output	The output is displayed as, Sum of a and b is 7. We can see that it is similar to our C code.
Errors Type int a = 2;	Now we will see some common errors which we can come across. Come back to our program. Suppose here I will declare variable a again, Type int a and a (semicolon) ;
On the terminal	Click on save. We have declared the variable a above the main function. And after the add function. Let us see what happens. Come back to the terminal.
Highlight Error	Now compile as before. We see errors Redifinition of int a int a previously defined here. Come back to our program. a is a global variable. It has a global scope. We cannot declare the variable twice as it is already declared globally We can only declare variable a as a local variable.
On the editor	Let us fix the error.
Delete int a = 2;	Delete this.
Click on save	Click on save.
On the terminal	Let us execute again. Come back to our terminal.
	Now compile as before Execute as before.
	Yes it is working. This brings us to the end of this tutorial.
Slide 5	Let us summarize, In this tutorial we learnt, Scope of variables Global variable eg. int a = 5; And Local variable eg. int sum;
Slide 6	As an assignment, Write a program to print the difference of two numbers.
Slide 7 About the Spoken Tutorial Project	Watch the video available at the link shown . It summarises the Spoken Tutorial project. If you do not have good bandwidth, you can download and watch it.
Slide 8 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 9 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 the link shown below: http://spoken-tutorial.org\NMEICT-Intro.
	This is Ashwini Patil from IIT Bombay signing off Thank You for joining.

Contributors and Content Editors

Ashwini