View source for Test/C2/Testing/English

Title of script:Preprocessor Directives in C

Author:Ashwini Patil

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



{| border="1"
!width="50%"| <center>Visual Cue</center>
!width="50%"| <center>Narration</center>
|-
|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 &lt;header file&gt;
|2)Header Files inclusion

       #include &lt;stdio.h&gt;:The functions and code ofstdio.h headeris included in the main program.

Syntax:

#Preprocessor Directive &lt;header file&gt;
|-
|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.
|}