0321537904_ppt73679-0321537904_pptSavitch_ch_08

Copyright2008PearsonAddison-Wesley.Allrightsreserved.,Chapter8,StringsandVectors,Slide8-3,Overview,8.1AnArrayTypeforStrings8.2TheStandardstringClass8.3Vectors,Copyright2008PearsonAddison-Wesley.Allrightsreserved.,8.1,AnArrayTypeforStrings,Slide8-5,AnArrayTypeforStrings,C-stringscanbeusedtorepresentstringsofcharactersC-stringsarestoredasarraysofcharactersC-stringsusethenullcharacter0toendastringTheNullcharacterisasinglecharacterTodeclareaC-stringvariable,declareanarrayofcharacters:chars11;,Slide8-6,DeclaringaC-stringaschars10createsspaceforonlyninecharactersThenullcharacterterminatorrequiresonespaceAC-stringvariabledoesnotneedasizevariableThenullcharacterimmediatelyfollowsthelastcharacterofthestringExample:,C-stringDetails,Slide8-7,C-stringDeclaration,TodeclareaC-stringvariable,usethesyntax:charArray_nameMaximum_C_String_Size+1;+1reservestheadditionalcharacterneededby0,Slide8-8,InitializingaC-string,ToinitializeaC-stringduringdeclaration:charmy_message20=Hithere.;Thenullcharacter0isaddedforyouAnotheralternative:charshort_string=abc;butnotthis:charshort_string=a,b,c;,Slide8-9,C-stringerror,ThisattempttoinitializeaC-stringdoesnotcausethe0tobeinsertedinthearraycharshort_string=a,b,c;,Slide8-10,DontChange0,DonottoreplacethenullcharacterwhenmanipulatingindexedvariablesinaC-stringIfthenullcharacterislost,thearraycannotactlikeaC-stringExample:intindex=0;while(our_stringindex!=0)our_stringindex=X;index+;Thiscodedependsonfindingthenullcharacter!,Slide8-11,SaferProcessingofC-strings,Thelooponthepreviousslidedependedonfindingthe0characterItwouldbewisertousethisversionincasethe0characterhadbeenremovedintindex=0;while(our_stringindex!=0,Slide8-12,AssignmentWithC-strings,Thisstatementisillegal:a_string=Hello;Thisisanassignmentstatement,notaninitializationTheassignmentoperatordoesnotworkwithC-strings,Slide8-13,AssignmentofC-strings,AcommonmethodtoassignavaluetoaC-stringvariableistousestrcpy,definedinthecstringlibraryExample:#includechara_string11;strcpy(a_string,Hello);PlacesHellofollowedbythenullcharacterina_string,Slide8-14,AProblemWithstrcpy,strcpycancreateproblemsifnotusedcarefullystrcpydoesnotcheckthedeclaredlengthofthefirstargumentItispossibleforstrcpytowritecharactersbeyondthedeclaredsizeofthearray,Slide8-15,ASolutionforstrcpy,ManyversionsofC+haveasaferversionofstrcpynamedstrncpystrncpyusesathirdargumentrepresentingthemaximumnumberofcharacterstocopyExample:charanother_string10;strncpy(another_string,a_string_variable,9);Thiscodecopiesupto9charactersintoanother_string,leavingonespacefor0,Slide8-16,=AlternativeforC-strings,The=operatordoesnotworkasexpectedwithC-stringsThepredefinedfunctionstrcmpisusedtocompareC-stringvariablesExample:#includeif(strcmp(c_string1,c_string2)coutStringsarenotthesame.;elsecoutStringarethesame.;,Slide8-17,strcmpslogic,strcmpcomparesthenumericcodesofelementsintheC-stringsacharacteratatimeIfthetwoC-stringsarethesame,strcmpreturns00isinterpretedasfalseAssoonasthecharactersdonotmatchstrcmpreturnsanegativevalueifthenumericcodeinthefirstparameterislessstrcmpreturnsapositivevalueifthenumericcodeinthesecondparameterislessNon-zerovaluesareinterpretedastrue,Slide8-18,MoreC-stringFunctions,Thecstringlibraryincludesotherfunctionsstrlenreturnsthenumberofcharactersinastringintx=strlen(a_string);strcatconcatenatestwoC-stringsThesecondargumentisaddedtotheendofthefirstTheresultisplacedinthefirstargumentExample:charstring_var20=Therain;strcat(string_var,inSpain);Nowstring_varcontainsTheraininSpain,strncatisasaferversionofstrcatAthirdparameterspecifiesalimitforthenumberofcharacterstoconcatenateExample:charstring_var20=Therain;strncat(string_var,inSpain,11);,Slide8-19,Display8.1(1),Display8.1(2),ThestrncatFunction,Slide8-20,C-stringsasArgumentsandParameters,C-stringvariablesarearraysC-stringargumentsandparametersareusedjustlikearraysIfafunctionchangesthevalueofaC-stringparameter,itisbesttoincludeaparameterforthedeclaredsizeoftheC-stringIfafunctiondoesnotchangethevalueofaC-stringparameter,thenullcharactercandetecttheendofthestringandnosizeargumentisneeded,Slide8-21,C-stringOutput,C-stringscanbeoutputwiththeinsertionoperatorExample:charnews=C-strings;coutnewsWow.canfillaC-stringWhitespaceendsreadingofdataExample:chara80,b80;coutab;coutabEndofOutput;couldproduce:Enterinput:Dobedotoyou!DobeEndofOutput,Slide8-23,ReadinganEntireLine,Predefinedmemberfunctiongetlinecanreadanentireline,includingspacesgetlineisamemberofallinputstreamsgetlinehastwoargumentsThefirstisaC-stringvariabletoreceiveinputThesecondisaninteger,usuallythesizeofthefirstargumentspecifyingthemaximumnumberofelementsinthefirstargumentgetlineisallowedtofill,Slide8-24,Usinggetline,ThefollowingcodeisusedtoreadanentirelineincludingspacesintoasingleC-stringvariablechara80;coutEnterinput:n;cin.getline(a,80);coutac_string;in_stream.getline(c_string,80);Replacecoutwiththenameofanoutput-filestreamout_streams1;skipswhitespaceandstopsonencounteringmorewhitespace,Slide8-43,getlineandTypestring,AgetlinefunctionexiststoreadentirelinesintoastringvariableThisversionofgetlineisnotamemberoftheistreamclass,itisanon-memberfunctionSyntaxforusingthisgetlineisdifferentthanthatusedwithcin:cin.getline()Syntaxforusinggetlinewithstringobjects:getline(Istream_Object,String_Object);,Slide8-44,getlineExample,Thiscodedemonstratestheuseofgetlinewithstringobjectsstringline;coutEnteralineofinput:n;getline(cin,line);coutlineENDOFOUTPUTn;Outputcouldbe:Entersomeinput:Dobedotoyou!Dobedotoyou!ENDOFOUTPUT,TheextractionoperatorcannotbeusedtoreadablankcharacterToreadonecharacteratatimeremembertousecin.getcin.getreadsvaluesoftypechar,nottypestringTheuseofgetline,andcin.getforstringinputaredemonstratedin,Slide8-45,Display8.5(1),Display8.5(2),CharacterInputWithstrings,Slide8-46,AnotherVersionofgetline,Theversionsofgetlinewehaveseen,stopreadingattheendoflinemarkerngetlinecanstopreadingatacharacterspecifiedintheargumentlistThiscodestopsreadingwhena?isreadstringline;couts2;cins2;,returns,getlineReturnsaReference,Slide8-48,getlineDeclarations,Thesearethedeclarationsoftheversionsofgetlineforstringobjectswehaveseenistream,Slide8-49,Mixingcinandgetline,RecallcinnskipswhitespacetofindwhatitistoreadthenstopsreadingwhenwhitespaceisfoundcinleavesthencharacterintheinputstreamExample:intn;stringline;cinn;getline(cin,line);leavesthenwhichimmediatelyendsgetlinesreadinglineissetequaltotheemptystring,Slide8-50,ignore,ignoreisamemberoftheistreamclassignorecanbeusedtoreadanddiscardallthecharacters,includingnthatremaininalineIgnoretakestwoargumentsFirst,themaximumnumberofcharacterstodiscardSecond,thecharacterthatstopsreadinganddiscardingExample:cin.ignore(1000,n);readsupto1000charactersorton,ThestringclassallowsthesameoperationsweusedwithC-stringsandmoreCharactersinastringobjectcanbeaccessedasiftheyareinanarraylast_nameiprovidesaccesstoasinglecharacterasinanarrayIndexvaluesarenotcheckedforvalidity!,Slide8-51,Display8.6,StringProcessing,Slide8-52,MemberFunctionlength,Thestringclassmemberfunctionlengthreturnsthenumberofcharactersinthestringobject:Example:intn=string_var.length();,atisanalternativetousingstoaccesscharactersinastring.atchecksforvalidindexvaluesExample:stringstr(Mary);coutstr6endl;coutstr.at(6)endl;str2=X;str.at(2)=X;,Slide8-53,Otherstringclassfunctionsarefoundin,Display8.7,MemberFunctionat,Slide8-54,Comparisonofstrings,ComparisonoperatorsworkwithstringobjectsObjectsarecomparedusinglexicographicorder(AlphabeticalorderingusingtheorderofsymbolsintheASCIIcharacterset.)=returnstrueiftwostringobjectscontainthesamecharactersinthesameorderRememberstrcmpforC-strings?,=canbeusedtocomparestringobjects,Slide8-55,ProgramExample:PalindromeTesting,ApalindromeisastringthatreadsthesamefromfronttobackasitdoesfrombacktofrontThisprogramignoresspacesandpunctuationUpperandlowercaseversionsoflettersareconsideredthesameletterExamples:AblewasIereIsawElba.Madam,ImAdam.Aman,aplan,acanal,Panama.Racecar,Slide8-56,PalindromeTesting:remove_punct,remove_punctremovespunctuationfromastringremove_punctcompareseachcharacterinthestringtothecharactersinastringcontainingallthepunctuationcharactersandthespacecharacter.Ifamatchisnotfound,thecharacterisaddedtothestringno_punctno_punct,theoriginalstringlessanypunctuationorspaces,isreturned,Slide8-57,PalindromeTesting:substr,Thesubstrmemberfunctionisusedtolocateasubstringwithinastringremove_punctusessubstrtoextractasinglecharacteratatimefromthesourcestring.Thecharacterisstoredina_char.remove_punctthenusesfunctionfindtoseeifthecharacterina_charisinthestringofpunctuationcharacters,Theentirepalindrometestingprogramisfoundin,Slide8-58,PalindromeTesting:TheProgram,Slide8-59,stringObjectstoC-strings,RecalltheautomaticconversionfromC-stringtostring:chara_c_string=C-string;string_variable=a_c_string;stringsarenotconvertedtoC-stringsBothofthesestatementsareillegal:a_c_string=string_variable;strcpy(a_c_string,string_variable);,Slide8-60,ConvertingstringstoC-strings,Thestringclassmemberfunctionc_strreturnstheC-stringversionofastringobjectExample:strcpy(a_c_string,string_variable.c_str();Thislineisstillillegala_c_string=string_variable.c_str();Recallthatoperator=doesnotworkwithC-strings,Slide8-61,Section8.2Conclusion,CanyouShowhowastringobjectcanbeusedlikeaC-string?Writecodetoreadanentirelineintoastringobject?Usethestringfunctionattoaccessindividualcharactersinastringobject?WritecodetoconvertastringtoaC-string?,Copyright2008PearsonAddison-Wesley.Allrightsreserved.,8.3,Vectors,Slide8-63,Vectors,VectorsarelikearraysthatcanchangesizeasyourprogramrunsVectors,likearrays,haveabasetypeTodeclareanemptyvectorwithbasetypeint:vectorv;identifiesvectorasatemplateclassYoucanuseanybasetypeinatemplateclass:vectorv;,Slide8-64,AccessingvectorElements,Vectorselementsareindexedstartingwith0sareusedtoreadorchangethevalueofanitem:vi=42;coutvi;scannotbeusedtoinitializeavectorelement,Slide8-65,InitializingvectorElements,Elementsareaddedtoavectorusingthememberfunctionpush_backpush_backaddsanelementinthenextavailablepositionExample:vectorsample;sample.push_back(0.0);sample.push_back(1.1);sample.push_back(2.2);,Slide8-66,ThesizeOfAvector,ThememberfunctionsizereturnsthenumberofelementsinavectorExample:Toprinteachelementofavectorgiventhepreviousvectorinitialization:for(inti=0;isample.size();i+)coutsampleiendl;,Slide8-67,TheTypeunsignedint,ThevectorclassmemberfunctionsizereturnsanunsignedintUnsignedintsarenonnegativeintegersSomecompilerswillgiveawarningifthepreviousfor-loopisnotchangedto:for(unsignedinti=0;isample.size();i+)coutsampleiendl;,Slide8-68,AlternatevectorInitialization,AvectorconstructorexiststhattakesanintegerargumentandinitializesthatnumberofelementsExample:vectorv(10);initializesthefirst10elementsto0v.size()wouldreturn10scannowbeusedtoassignelements0through9push_backisusedtoassignelementsgreaterthan9,Slide8-69,VectorInitializationWithClasses,ThevectorconstructorwithanintegerargumentInitializeselementsofnumbertypestozeroInitializeselementsofclasstypesusingthedefaultconstructorfortheclass,TousethevectorclassIncludethevectorlibrary#includeVectornamesareplacedinthestandardnamespacesotheusualusingdirectiveisneeded:usingnamespacestd;,Slide8-70,Display8.9,ThevectorLibrary,Slide8-71,vectorIssues,AttemptingtousetosetavaluebeyondthesizeofavectormaynotgenerateanerrorTheprogramwillprobablymisbehaveTheassignmentoperatorwithvectorsdoesanelementbyelementcopyoftherighthandvectorForclasstypes,theassignmentoperatormustmakeindependentcopies,Slide8-72,vectorEfficiency,Avectorscap