Preprocessor Directive in C

TO UNDERSTAND about Preprocessor Directives IN C.
TO LEARN ABOUT #define.
TO LEARN ABOUT how to use macro with arguments.
To learn about file inclusion.
To learn about Conditional Compilation.
To learn about #pragma in C
TO LEARN ABOUT #if define and #ifndefine in C.
TO LEARN ABOUT #undef in C.
TO LEARN ABOUT # and ## in C Language.

1. PAPER: INTRODUCTION PROGRAMMING LANGUAGE USING C
PAPER ID: 20105
PAPER CODE: BCA 105
DR. VARUN TIWARI
(ASSOCIATE PROFESSOR)
(DEPARTMENT OF COMPUTER SCIENCE)
BOSCO TECHNICAL TRAINING SOCIETY,
DON BOSCO TECHNICAL SCHOOL, OKHLA ROAD , NEW DELHI

2. C PREPROCESSOR
DIRECTIVE

3. OBJECTIVES
IN THIS CHAPTER YOU WILL LEARN:
1.TO UNDERSTAND ABOUT PREPROCESSOR DIRECTIVES IN C.
2.TO LEARN ABOUT #DEFINE.
3.TO LEARN ABOUT HOW TO USE MACRO WITH ARGUMENTS.
4.TO LEARN ABOUT FILE INCLUSION.
5.TO LEARN ABOUT CONDITIONAL COMPILATION.
6.TO LEARN ABOUT #PRAGMA IN C
7.TO LEARN ABOUT #IF DEFINE AND #IFNDEFINEIN C.
8.TO LEARN ABOUT #UNDEFIN C.
9.TO LEARN ABOUT # AND ## IN C LANGUAGE.

4. PREPROCESSORDIRECTIVE:CPROVIDEAVERYUSEFULFACILITYOFMACROSUBSTITUTION.THISENABLES
THEPROGRAMMERTOWRITECODEWHOISMOREREADABLETHANTHECRYPTICWAY.THECCOMPILER
HASAPREPROCESSORWHICHNEEDSTHESOURCECODESANDTHUSSOMEPROCESSINGBEFORE
PASSINGINTOTHECOMPILERFORTHEPURPOSEOFCOMPILATION.THEREAREAFEWPROCESSOR
COMMANDWHICHITCANINTERPRETER.THEYARENOTANORMALCCOMMAND.THEREARESIGNEDBY
PUTTING#INTHEFIRSTCOLUMNFOLLOWEDBYAKEYWORD.WHICHSHOULDAVALIDONEEXCEPTED
BYTHEPREPROCESSOR.
CPREPROCESSORISAPROGRAMTHATPROCESSESOURPROGRAMBEFOREITISPASSEDTOTHE
COMPILER.BEFORECPROGRAMISCOMPILED,ITISPASSEDTHROUGHANOTHERPROGRAMCALLED
“PREPROCESSOR”.THECPROGRAMISKNOWNAS‘SOURCECODE’.THEPREPROCESSORWORKSONTHE
SOURCECODEASPERTHEPREPROCESSORDIRECTIVESUSEDINTHESOURCECODE.EACHPREPROCESSOR
DIRECTIVEBEGINSWITHA#SYMBOL.
(A).MACROEXPANSION
(B).FILEINCLUSION
(C).CONDITIONALCOMPILATION
(D).MISCELLANEOUSDIRECTIVES

6. #DEFINE:ITISUSEDTODEFINEACONSTANTORMACRO.ITPROVIDEAFACILITYFORMACROSUBSTITUTION.WECANDEFINEANIDENTIFIERAND
ATTACHEDASTRINGTOIT.THEPREPROCESSORSCANTHECOMPLETEPROGRAM&REPLACEALLTHEOCCURRENCEOFTHEIDENTIFIERWITHTHESTRING
ATTACHEDTOITWITHTHEIDENTIFIERUSEDARERECOMMENDEDTOBEWRITTENINUPPERCASELETTER.
EXAMPLE-:
#include<stdio.h>
#include<conio.h>
#definemax20
voidmain(){
charname[max];
clrscr();
printf("\nenteryourname-:");
gets(name);
//puts(name);
printf("mynameis-:%s",name);
getch();}
Output:
enteryourname-:varunTiwari
Mynameis-:varuntiwari

7. #DEFINEWORKSLIKEMACRO:
EXAMPLE:
#include<stdio.h>
#include<conio.h>
#definePRINTprintf(“\nMynameisRahul.Iam22yearsOld”);
voidmain(){
clrscr();
PRINT;
getch();
}
Output:
My name is Rahul. I am 22 years Old.

8. MACROWITHARGUMENTS:THEMACROTHATWEHAVEUSEDSOFARARECALLEDSIMPLEMACRO.
MACROSCANHAVEARGUMENTS,JUSTASFUNCTIONSCAN.

10. FILEINCLUSION:ITSIMPLYCAUSESTHEENTIRECONTENTSOFFILENAMETOBEINSERTEDINTOTHE
SOURCECODEWHEREWEHAVEUSED#INCLUDE.ITISCOMMONFORTHEFILESTHATARETOBE
INCLUDEDTOHAVEA.HEXTENSION.
SYNTAX:#include“filename”
#include“minmax.h”

12. CONDITIONALCOMPILATION:WECAN,IFWEWANT,HAVETHECOMPILERSKIPOVERPARTOFA
SOURCECODEBYINSERTINGTHEPREPROCESSINGCOMMANDS.CPROVIDEYOUANOOF
CONDITIONALCOMPILATIONPREPROCESSORDIRECTIVE.
1.#IF#ENDIF
2.#IF#ELSE#ENDIF
3.#IF#ELIF#ENDIF
4.#IF#ELSE#IF#ENDIF
5.#IFDEFAND#IFNDEF
IFMACRONAMEHASBEEN#DEFINE,THEBLOCKOFCODEWILLBEPROCESSEDASUSUAL,
OTHERWISENOT.
SYNTAX:#IFEXPRESSION
STATEMENT1;
STATEMENT2;
STATEMENT3;
#ENDIF

14. II.#IF#ELSE
SYNTAX:#IFEXPRESSION
STATEMENT1;
STATEMENT2;
STATEMENT3;
#ELSE
STATEMENT1;
STATEMENT2;
STATEMENT3;
#ENDIF

16. III.#IF#ELIF#ENDIF
SYNTAX:#IFEXPRESSION
STATEMENT1;
STATEMENT2;
STATEMENT3;
#ELIF
STATEMENT1;
STATEMENT2;
STATEMENT3;
#ENDIF

18. IV.#IF#ELSE#IF#ENDIF
SYNTAX:#IFEXPRESSION
STATEMENT;
#ELSE
#IFEXPRESSION
STATEMENT;
#ELSE
#IFEXPRESSION
STATEMENT;
#ENDIF
#ENDIF
#ENDIF

20. V.#IFDEFAND#IFNDEF:IFTHEMACRONAMEISDEFINEDTHENITRETURNTRUE(NONZERO)ELSEIF
THEMACRONAMEISNOTDEFINEDITRETURNFALSE(ZERO).
SYNTAX:#IFDEFMACRONAME
STATEMENT;
#ENDIF
SYNTAX:#IFNDEFMACRONAME
STATEMENT;
#ENDIF

23. MISCELLANEOUSDIRECTIVES:CPROVIDEYOUSOMEOTHERDIRECTIVEWHICHISVERYHELPFULFOR
USER.
1.#UNDEF
2.#PRAGMA
3.#AND##
1.#UNDEF:ONESOMEOCCASIONITMAYBEDESIRABLETOCAUSEADEFINEDNAMETOBECOME
UNDEFINEDTHISCANBEACCOMPLISHEDBYMEANSOFTHE#UNDEFDIRECTIVE.
SYNTAX:
#UNDEF(MACRONAME)

25. 2.#PRAGMA:THE#PRAGMAISANIMPLEMENTATIONORIENTEDDIRECTIVETHATALLOWSUSTO
SPECIFYVARIOUSINSTRUCTIONTOBEGIVENTOTHECOMPILER.USING#PRAGMA,YOUCANVARY
ONECOMPILERTOANOTHERCOMPILERTHEREARECERTAINPROGRAMAVAILABLEWITHMICROSOFT
CCOMPILERWHICHDEALWITHFORMATTINGSOURCELISTING&PLACINGCOMMANDSINTHEOBJECT
FILEGENERATEDBYTHECOMPILER.TURBOCCOMPILERHASGOTAPRAGMAWHICHALLOWSYOUTO
WRITEASSEMBLYSTATEMENTINYOURCPROGRAM.DECLARATIONOFPRAGMAGIVENBELOW:
1.#PRAGMASTARTUPAND#PRAGMAEXIT:THESEDIRECTIVESALLOWUSTOSPECIFYFUNCTIONS
THATARECALLEDUPONPROGRAMSTARTUP(BEFOREMAIN())ORPROGRAMEXIT(JUSTBEFORE
THEPROGRAMTERMINATES).THEYUSAGEISASFOLLOW:
2.#PRAGMAWARN:ONCOMPILATIONTHECOMPILERREPORTSERRORSANDWARNINGSINTHE
PROGRAM.IFANYERRORSHAVETOBECORRECTED.WARNINGS,ONTHEOTHERHAND,OFFER
THEPROGRAMMER AHINTORSUGGESTIONTHATSOMETHINGMAYBEWRONGWITHA
PARTICULARPIECEOFCODE.

26. SYNTAX:
#PRAGMASTARTUPFUNCTIONNAME
#PRAGMAEXITFUNCTIONNAME
EXAMPLE:
#PRAGMASTARTUPADD()
#PRAGMAEXITSUB()

29. 2.#:THE#OPERATORISCALLEDSTRINGIZINGOPERATOR.THISOPERATORISUSEDTOCONVERT
ANYTEXTINTOSTRINGWITHOUTUSINGANYQUOTES.
EXAMPLE:

30. 2.##:THE##OPERATORISCALLEDTOKENPASTINGOPERATOR.THISOPERATORISUSEDTOADDOR
CONCATETWOTOKENSINTOONESTRING.
EXAMPLE:

31. THANK YOU