C程序设计语言英文版已改格式汇总.docx

C程序设计语言英文版已改格式汇总.docx

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C程序设计语言英文版已改格式汇总

CHAPTER1-ATUTORIALINTRODUCTION

LetusbeginwithaquickintroductioninC.Ouraimistoshowtheessentialelementsofthelanguageinrealprograms,butwithoutgettingboggeddownindetails,rules,andexceptions.Atthispoint,wearenottryingtobecompleteorevenprecise（savethattheexamplesaremeanttobecorrect）.Wewanttogetyouasquicklyaspossibletothepointwhereyoucanwriteusefulprograms,andtodothatwehavetoconcentrateonthebasics:

variablesandconstants,arithmetic,controlflow,functions,andtherudimentsofinputandoutput.WeareintentionallyleavingoutofthischapterfeaturesofCthatareimportantforwritingbiggerprograms.Theseincludepointers,structures,mostofC'srichsetofoperators,severalcontrol-flowstatements,andthestandardlibrary.

Thisapproachanditsdrawbacks.Mostnotableisthatthecompletestoryonanyparticularfeatureisnotfoundhere,andthetutorial,bybeingbrief,mayalsobemisleading.AndbecausetheexamplesdonotusethefullpowerofC,theyarenotasconciseandelegantastheymightbe.Wehavetriedtominimizetheseeffects,butbewarned.Anotherdrawbackisthatlaterchapterswillnecessarilyrepeatsomeofthischapter.Wehopethattherepetitionwillhelpyoumorethanitannoys.

Inanycase,experiencedprogrammersshouldbeabletoextrapolatefromthematerialinthischaptertotheirownprogrammingneeds.Beginnersshouldsupplementitbywritingsmall,similarprogramsoftheirown.BothgroupscanuseitasaframeworkonwhichtohangthemoredetaileddescriptionsthatbegininChapter2.

1.1GETTINGSTARTED

Theonlywaytolearnanewprogramminglanguageisbywritingprogramsinit.Thefirstprogramtowriteisthesameforalllanguages:

Printthewords

hello,world

Thisisabighurdle;toleapoverityouhavetobeabletocreatetheprogramtextsomewhere,compileitsuccessfully,loadit,runit,andfindoutwhereyouroutputwent.Withthesemechanicaldetailsmastered,everythingelseiscomparativelyeasy.

InC,theprogramtoprint''hello,world''is

#include

main（）

{

printf（"hello,world\n"）;

}

Justhowtorunthisprogramdependsonthesystemyouareusing.Asaspecificexample,ontheUNIXoperatingsystemyoumustcreatetheprograminafilewhosenameendsin''.c'',suchashello.c,thencompileitwiththecommand

cchello.c

Ifyouhaven'tbotchedanything,suchasomittingacharacterormisspellingsomething,thecompilationwillproceedsilently,andmakeanexecutablefilecalleda.out.Ifyouruna.outbytypingthecommand

a.out

itwillprint

hello,world

Onothersystems,theruleswillbedifferent;checkwithalocalexpert.

Now,forsomeexplanationsabouttheprogramitself.ACprogram,whateveritssize,consistsoffunctionsandvariables.Afunctioncontainsstatementsthatspecifythecomputingoperationstobedone,andvariablesstorevaluesusedduringthecomputation.CfunctionsarelikethesubroutinesandfunctionsinFortranortheproceduresandfunctionsofPascal.Ourexampleisafunctionnamedmain.Normallyyouareatlibertytogivefunctionswhatevernamesyoulike,but''main''isspecial-yourprogrambeginsexecutingatthebeginningofmain.Thismeansthateveryprogrammusthaveamainsomewhere.

mainwillusuallycallotherfunctionstohelpperformitsjob,somethatyouwrote,andothersfromlibrariesthatareprovidedforyou.Thefirstlineoftheprogram,

#include

tellsthecompilertoincludeinformationaboutthestandardinput/outputlibrary;thelineappearsatthebeginningofmanyCsourcefiles.ThestandardlibraryisdescribedinChapter7andAppendixB.

Onemethodofcommunicatingdatabetweenfunctionsisforthecallingfunctiontoprovidealistofvalues,calledarguments,tothefunctionitcalls.Theparenthesesafterthefunctionnamesurroundtheargumentlist.Inthisexample,mainisdefinedtobeafunctionthatexpectsnoarguments,whichisindicatedbytheemptylist（）.

Thestatementsofafunctionareenclosedinbraces{}.Thefunctionmaincontainsonlyonestatement,

printf（"hello,world\n"）;

Afunctioniscalledbynamingit,followedbyaparenthesizedlistofarguments,sothiscallsthefunctionprintfwiththeargument"hello,world\n".printfisalibraryfunctionthatprintsoutput,inthiscasethestringofcharactersbetweenthequotes.

Asequenceofcharactersindoublequotes,like"hello,world\n",iscalledacharacterstringorstringconstant.Forthemomentouronlyuseofcharacterstringswillbeasargumentsforprintfandotherfunctions.

Thesequence\ninthestringisCnotationforthenewlinecharacter,whichwhenprinted

advancestheoutputtotheleftmarginonthenextline.Ifyouleaveoutthe\n（aworthwhileexperiment）,youwillfindthatthereisnolineadvanceaftertheoutputisprinted.Youmustuse\ntoincludeanewlinecharacterintheprintfargument;ifyoutrysomethinglike

printf（"hello,world"）;

theCcompilerwillproduceanerrormessage.

printfneversuppliesanewlinecharacterautomatically,soseveralcallsmaybeusedtobuildupanoutputlineinstages.Ourfirstprogramcouldjustaswellhavebeenwritten

#include

main（）

{

printf（"hello,"）;

printf（"world"）;

printf（"\n"）;

}

toproduceidenticaloutput.

Noticethat\nrepresentsonlyasinglecharacter.Anescapesequencelike\nprovidesageneralandextensiblemechanismforrepresentinghard-to-typeorinvisiblecharacters.

AmongtheothersthatCprovidesare\tfortab,\bforbackspace,\"forthedoublequoteand\\forthebackslashitself.ThereisacompletelistinSection2.3.

Exercise1-1.Runthe''hello,world''programonyoursystem.Experimentwithleavingoutpartsoftheprogram,toseewhaterrormessagesyouget.

Exercise1-2.Experimenttofindoutwhathappenswhenprints'sargumentstringcontains\c,wherecissomecharacternotlistedabove.

1.2VARIABLESANDARITHMETICEXPRESSIONS

ThenextprogramusestheformulaoC=（5/9）（oF-32）toprintthefollowingtableofFahrenheit

temperaturesandtheircentigradeorCelsiusequivalents:

1-17

20-6

404

6015

8026

10037

12048

14060

16071

18082

20093

220104

240115

260126

280137

300148

Theprogramitselfstillconsistsofthedefinitionofasinglefunctionnamedmain.Itislongerthantheonethatprinted''hello,world'',butnotcomplicated.Itintroducesseveralnewideas,includingcomments,declarations,variables,arithmeticexpressions,loops,andformattedoutput.

#include

/*printFahrenheit-Celsiustableforfahr=0,20,...,300*/

main（）

{

intfahr,celsius;

intlower,upper,step;

lower=0;/*lowerlimitoftemperaturescale*/

upper=300;/*upperlimit*/

step=20;/*stepsize*/

fahr=lower;

while（fahr<=upper）{

celsius=5*（fahr-32）/9;

printf（"%d\t%d\n",fahr,celsius）;

fahr=fahr+step;

}

}

Thetwolines

/*printFahrenheit-Celsiustable

forfahr=0,20,...,300*/

areacomment,whichinthiscaseexplainsbrieflywhattheprogramdoes.Anycharactersbetween/*and*/areignoredbythecompiler;theymaybeusedfreelytomakeaprogrameasiertounderstand.Commentsmayappearanywherewhereablank,tabornewlinecan.InC,allvariablesmustbedeclaredbeforetheyareused,usuallyatthebeginningofthefunctionbeforeanyexecutablestatements.Adeclarationannouncesthepropertiesofvariables;itconsistsofanameandalistofvariables,suchas

intfahr,celsius;

intlower,upper,step;

Thetypeintmeansthatthevariableslistedareintegers;bycontrastwithfloat,whichmeansfloatingpoint,i.e.,numbersthatmayhaveafractionalpart.Therangeofbothintandfloatdependsonthemachineyouareusing;16-bitsints,whichliebetween-32768and+32767,arecommon,asare32-bitints.Afloatnumberistypicallya32-bitquantity,withatleastsixsignificantdigitsandmagnitudegenerallybetweenabout10-38and1038.Cprovidesseveralotherdatatypesbesidesintandfloat,including:

charcharacter-asinglebyte

shortshortinteger

longlonginteger

doubledouble-precisionfloatingpoint

Thesizeoftheseobjectsisalsomachine-dependent.Therearealsoarrays,structuresandunionsofthesebasictypes,pointerstothem,andfunctionsthatreturnthem,allofwhichwewillmeetinduecourse.

Computationinthetemperatureconversionprogrambeginswiththeassignmentstatements

lower=0;

upper=300;

step=20;

whichsetthevariablestotheirinitialvalues.Individualstatementsareterminatedbysemicolons.

Eachlineofthetableiscomputedthesameway,soweusealoopthatrepeatsonceperoutputline;thisisthepurposeofthewhileloop

while（fahr<=upper）{

...

}

Thewhileloopoperatesasfollows:

Theconditioninparenthesesistested.Ifitistrue（fahrislessthanorequaltoupper）,thebodyoftheloop（thethreestatementsenclosedinbraces）isexecuted.Thentheconditionisre-tested,andiftrue,thebodyisexecutedagain.Whenthetestbecomesfalse（fahrexceedsupper）theloopends,andexecutioncontinuesatthestatementthatfollowstheloop.Therearenofurtherstatementsinthisprogram,soitterminates.

Thebodyofawhilecanbeoneormorestatementsenclosedinbraces,asinthetemperatureconverter,orasinglestatementwithoutbraces,asin

while（i

i=2*i;

Ineithercase,wewillalwaysindentthestatementscontrolledbythewhilebyonetabstop（whichwehaveshownasfourspaces）soyoucanseeataglancewhichstatementsareinsidetheloop.Theindentationemphasizesthelogicalstructureoftheprogram.AlthoughCompilersdonotcareabouthowaprogramlooks,properindentationandspacingarecriticalinmakingprogramseasyf