Test/C2/Testing/English

Title of script:Preprocessor Directives in C

Author:Ashwini Patil

Keywords:Video tutorial, #include, #define, #if, #undef, #else, #endif

Visual Cue	Narration
Display Slide 1	Welcome to the Spoken Tutorial on Preprocessor Directives in C
Display Slide 2	In this tutorial, we will learn about Preprocessor Directives #include #define #if #else #undefwith the help of examples.
Display Slide 3 System Requirements	For this tutorial I am using Ubuntu Operating System version 11.10 gcc  Compiler version 4.6.1 on Ubuntu
Display Slide 4 Prerequisites spoken-tutorial.org	To follow this tutorial you should be familiar with  C tutorials. If not, for relevant tutorials please visit spoken hyphen tutorial dot org.
	I will start with an introduction toPreprocessor Directives.
Display Slide 5-6 Introduction	The preprocessor Directivesmodifies a source file before compilation. All preprocessor Directivesbegins with a #symbol. It instructsCcompiler to do pre-processing before compilation. It makes the programs easier to read, modify and develop It makes the code portable and helps to customize the code.
Display Slide 7 Syntax: Preprocessor Directive	There are different types ofPreprocessor Directives. 1) Defining preprocessor directives. define:This macro defines constant values.     Macro:Macro is a code block with a given name. To use the code block we have to use the name of the macro.        #undef:This is used to undefine the definedmacro Syntax: Preprocessor Directive
Display Slide 8 Syntax: Preprocessor Directive <header file>	2)Header Files inclusion        #include <stdio.h>:The functions and code ofstdio.h headeris included in the main program. Syntax: Preprocessor Directive <header file>
Display Slide 9	3)Conditional compilation        Check for condition before compilation        #ifdef:This checks whether a macro is defined in the program or not.            If yes then the if clause is statements are added in the program.        #else:If the macro is not defined the else part is added.        #endif:This ends the preprocessor conditions.
	Let us go through an example code.
Point to the filename.	Note that our filename isarea.c In this program, we will calculate the area of a circle.
define radius 15 define pi 3.14	Here we have defined a constant value for radiusand pi using#define keyword. Then we calculate the area of the circle and print the result.
Type: gcc area.c -o area ./area	Let us execute the program. On the terminal. Type: gcc area.c -o area ./area
Highlight Output	The output is: Radius of circle : 15 Value of pi : 3.140000 Area of the circle : 706.500000
	Now let us see an example onconditional directives. We will use the same example.
Type: ifdef radius { close the brackets after the lastprintf statement }	I will add a few lines here. In main function type: ifdef radius (opening bracket) { close the brackets after the lastprintf statement }
type: else {    printf(“Radius of the circle is not defined”); } endif	Now after the closing bracket type: else (opening bracket){    printf(“Radius of the circle is not defined”); (closing bracket)} endif
On the terminal	Click onSave. Let us execute again. On the terminal press the up-arrow key twice. Again press the up-arrow key twice.
Highlight the output	We see the same output. Radius of circle : 15 Value of pi : 3.140000 Area of the circle : 706.500000
Comment //#define radius 15.	Now come back to the terminal. Let us comment the second line //#define radius 15. Click onSave. On the terminal. Execute again.
Highlight Output	We see, Radius of circle not defined.
	Now let us see the use of#undef derivative. Come back to out program Now insideifcondition,I will undefine theradius. And redefine it with a new value
Type undef radius define radius 20	Type: undef radius define radius 20
Highlight output	Now click onSave. Let us execute on terminal. Press the uparrow key twice Again Press the uparrow key twice You can see the output as: Radius of circle : 20 Value of pi : 3.140000 Area of the circle : 1256.000000
	This brings us to the end of this tutorial. Let us summarize.
Display Slide 13 Summary	In this tutorial we learnt, Preprocessor Directives #include #define #if #else #undef
Display Slide 14	As an assignment, write a program to calculate the factorial of a number. Define the number using#define keyword
Display Slide 15	Watch the video available at the link shown below It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Display Slide 16 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
Display Slide 15 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 from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Ashwini