1.1.7C程序与程序设计简介 - C程序与程序设计简介1.1

TheCProgrammingLanguage典型程序设计语言的排行HistoryofCEarlydevelopmentsAT&TBellLabs,1969-1973DennisMacAlistairRitchie(DMR)TransplantUnixfromPDP-7toPDP-11withKennethLaneThompson(Ken)Add”struct”into,1973MostoftheUnixkernelwasrewritteninCK&RC:In1978,”TheCProgrammingLanguage”BrianKernighanandDennisRitchieStandardI/Olibrary(MikeLesk)Longintdatatype,unsignedintdatatype,compoundassignmentoperators=opKen&Ritchie

---1998NationalMedalofTechnologyfromBillClinton

ANSICandISOCC89,1983,ANSI;C99,1990,ISOFunctionprototypes,voidpointersinternationalcharactersetsandlocalespreprocessorenhancementsC99ISO/IEC9899:1999,1999inlinefunctionsseveralnewdatatypes(includinglonglongintandacomplextypetorepresentcomplexnumbers)variable-lengtharrays...C1x,workhasbegunsince2007IntroductionCisageneral-purposeprogramminglanguageCprovidesthefundamentalcontrol-flowconstructionsCisarelatively“low-level”languageCprovidesnooperationstodealdirectlywithcompositeobjectsCoffersonlystraightforward,single-threadcontrolflowCisindependentofanyparticularmachinearchitectureSomeofCoperatorshavethewrongprecedenceSomepartsoftheCsyntaxcouldbebetterChapter1.ATutorialIntroductionLetusbeginwithaquickintroductiontoCWritingaprograminCtoprintthewords:hello,worldInC，theprogramtoprint”hello,world”is:#include<stdio.h>

main(){

printf(“hello,world\n”);}------------------------------------------------------------------------InPASCAL,theprogramwouldbe:Programhello(output);beginwriteln(‘hello,world’)end.includeinformationaboutstandardlibrarymainfunctionwithnoargumentscalllibraryfunctionnamedprintfstatementsofmainareenclosedinbraceTheprogramwouldbewritten:

#include<stdio.h> main() {

printf(“hello,”);

printf(“world”);

printf(“\n”); }

1.2VariablesandArithmeticExpressionsInC,allvariablesmustbedeclearedbeforetheyareused.Formats:typevariablesExamples intfahr,celsius; intlower,upper,step; floattotal;InC,anexpressioniscomposedwith:constantsvariablesfunctionsoperatorsExamples fahr=fahr+step1.2VariablesandArithmeticExpressionsProgramExamplesFahrenheit Celsius0-1720-640460158026100371204814060160711808220093220104260126280137300148

Program：#include<stdio.h> /*printfFahrenheit-Celsiustable

forfahr=0,20,40,…,300*/main(){ intfahr,celsius; intlower,upper,step; lower=0; /*lowerlimitofTtable*/ 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; }}1.2VariablesandArithmeticExpressionsTheprintfusefulformat:%d printasdecimalinteger;%6d printasdecimalinteger,asatleast6characterswide;%f printasfloatingpoint;%6f printasfloatingpoint,asatleast6characterswide;%.2f printasfloatingpoint,2charactersafterdecimal point;%6.2fprintasfloat,atleast6wideand2charactersafter decimalpoint;%o printasoctal;%x printashexadecimal;%c printasacharacter; %s printascharacterstring;%% print%itself

1.3TheFORstatementRewritedprogramoftemperatureconverterusingFOR:#include<stdio.h>/*printFahrenheit-Celsiustable*/ main() { intfahr; for(fahr=0;fahr<=300;fahr=fahr+20)printf(“%3d%6.1f\n”,fahr,(5.0/9.0)*(fahr-32)); }1.4SymbolicConstantsSymbolicConstantsisaparticularstringofcharacters.Format：

#definenamereplacement-textFunction:

Anyoccurrenceofnamewillbereplacedbythecorrespondingreplacement-text.Examples:

#defineLOWER0/*lowerlimitoftable*/ #defineUPPER300/*upperlimitoftable*/ #defineSTEP20/*steplimitoftable*/ /*printFahrenheit-Celsiustable*/ main() {

int

fahr; for(fahr=LOWER;fahr<=UPPER;fahr=fahr+STEP)

printf(“%3d%6.1f\n”,fahr,(5.0/9.0)*(fahr-32)); }1.5CharacterInputandOutputImportantView:

InC,themodelofInput&Outputaresupportedbythestandardlibrary,andNOTthestatementsofC.ThisisverydifferentofPASCAL.

TowsimplestI/Ofunctions: .getchar()——readoncharacteratatimefrom textstream

c=getchar(); .putchar()——writeonecharacteratatimefrom textstream

putchar(c);1.5CharacterInputandOutputFileCopyingAlgorithmProgram:

#include<stdio.h> /*copyinputtooutput;1stversion*/ main() { intc; c=getchar(); while(c!=EOF){ putchar(c); c=getchar(); } }readacharacterwhile(characterisnotend-of-fileindicator)outputthecharacterjustreadreadacharacter1.5CharacterInputandOutputFilecopyingprogram(2nd

version) #include<stdio.h> /*copyinputtooutput;2ndversion*/ main() { intc; while((c=getchar())!=EOF) putchar(c); }NOTE:c=getchar()!=EOFiseauivalenttoc=(getchar()!=EOF)1.5CharacterInputandOutput

CharacterCountingVersion1 Version2++meansincrementbyone.++ncnc=nc+1#include<stdio.h>main(){longnc;nc=0;while(getchar()!=EOF)++nc;printf(“%ld\n”,nc);}#include<stdio.h>main(){doublenc;for(nc=0;getchar()!=EOF;++nc);printf(“%.0f\n”,nc);}1.5CharacterInputandOutputLineCounting#include<stdio.h> /*countlinesininput*/ main() { intc,nl; nl=0; while((c=getchar())!=EOF) if(c==‘\n’) ++nl; printf(“%d\n”,nl); }1.5CharacterInputandOutputWordCounting:#include<stdio.h> #defineIN1 /*insideaword*/ #defineOUT0 /*outsideaword*/ /*countlines,wordsandcharactersininput*/1.5CharacterInputandOutput

main() {

intc,nl,nw,nc,state; state=OUT;

nl=nw=nc=0;

while((c=getchar())!=EOF){ ++nc;

if(c==

‘\n’)++nl;

if(c==‘’||c==‘\n’||c==‘\t’) state=OUT; elseif(state==OUT){ state=IN;++nw; } }

printf(“%d%d%d\n”,nl,nw,nc); }1.6ArraysArrayExample:Tocountdigits,whitespaces,others.

#include<stdio.h>main(){

int

c,I,nwhite,nother;

intndigit[10];

nwhite=nother=0;

for(i=0;i<10;++i)

ndigit[i]=0;

while((c=getchar())!=EOF)

if(c>=‘0’&&c<=‘9’) ++ndigit[c-’0’]; elseif(c==‘’&&c==‘\n’||c==‘\t’) ++nwhite;

else ++nother;

printf(“digits=“);

for(i=0;i<10;i++)

printf(“%d”,ndigit[i]);

printf(“,whitespace=%d,other=%d\n”,nwhite,nother);}1.7FunctionsFunctiondefinitionform:

return-typefunction-name(parameterdeclarations,ifany) { declarations statements }1.7FunctionsExample:calln-thpower.#include<stdio.h>int

power(int

m,intn);main(){

inti;

for(i=0;i<10;i++)

printf(“%d%d%d\n”,i,power(2,i),

power(-3,i));

return0; }/*power:raisebaseton-thpower:n>=0*/intpower(intbase,intn){

inti,p; p=1;

for(i=1;i<=n;++i) p=p*base; returnp;}1.7Functions/*power:raisebaseton-thpower;n>=0*//* (old-styleversion) */power(base,n)intbase,n;{ inti,p; p=1; for(i=1;i<=n;++i) p=p*base; returnp;}1.8Arguments——callbyValueInC,allfunctionargumentsarepassed“byvalue”/*power:raisebaseton-thpower;n>=0;version2*/intpower(intbase,intn){ intp; for(p=1;n>0;--n) p=p*base; returnp;}1.9CharacterArraysExample:readsasetoftextlinesandprintsthelongestAlgorithm:Program:

while(there’sanotherline)

if(it’slongerthanthepreviouslongest) saveit saveitslengthprintlongestline#include<stdio.h>#defineMAXLINE1000/*maxinuminputlinesize*/int

getline(charline[],int

maxline);voidcopy(charto[],charfrom[]);main(){

int

len,max; charline[MAXLINE],longest[MAXLINE]; max=0; while((len=getline(line,MAXLINE))>0

if(len>max) {max=len;copy(longest,line);}

if(max>0)/*therewasaline*/

printf(“%s”,longes