StructuresinC++IntroductiontoLinkedLists

CS16:SolvingProblemswithComputersILecture#14

ZiadMatni

Dept.ofComputerScience,UCSB

LectureOutlineStructures (Ch.10.1)•  Definingstructures•  Membervariablesandfunctions•  Structuresinfunctions•  Hierarchyinstructures•  Initializingstructures

LinkedLists(Ch.13.1)•  Wewillcovereverythinginthissection

– WearenotcoveringCh.13.2section!

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First…WhatIsaClass?

•  Aclassisadatatypewhosevariablesarecalledobjects

•  Somepre-defineddatatypesyouhaveusedare:int,char,double

•  Somepre-definedclassesyouhaveusedare:ifstream,string,vector

•  Youcanalsodefineyourownclassesaswell

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ClassDefinitions

•  Todefinea“class”,weneedto…– Describethekindsofvaluesthevariablecanhold•  Numbers?Characters?Both?Somethingelse?

– Describethememberfunctions• Whatcanwedowiththesevalues?

•  Wewillstartbydefiningstructuresasafirststeptowarddefiningclasses

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STRUCTURES

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Structures

•  Astructure’susecanbeviewedasanobject

•  Let’ssayitdoesnotcontainanymemberfunctions(fornow…)

•  Itdoescontainmultiplevaluesofpossiblydifferenttypes

•  We’llcallthesemembervariables

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StructuresforData

•  Thesemultiplevaluesarelogicallyrelatedtooneanotherandcometogetherasasingleitem–  Examples:AbankCertificateofDeposit(CD)whichhasthefollowingvalues: abalance aninterestrate aterm(howmanymonthstomaturity)

–  Astudentrecordwhichhasthefollowingvalues: thestudent’sIDnumber thestudent’slastname thestudent’sfirstname thestudent’sGPA5/24/18 Matni,CS16,Sp18 7

Whatkindofvaluesshouldthese

individuallybe?!

Whatkindofvaluesshouldthese

individuallybe?!

TheCDStructureExample:Definition•  TheCertificateofDepositstructurecanbedefinedas

structCDAccount

{ doublebalance; //adollaramount

doubleinterest_rate; //apercentage intterm; //atermamountinmonths

};

•  Keywordstructbeginsastructuredefinition•  CDAccountisthestructuretag–thisisthestructure’stype•  Membernamesareidentifiersdeclaredinthebraces

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Remember this semicolon!

UsingtheStructure

•  Structuredefinitionshouldbeplacedoutsideanyfunctiondefinition–  Includingoutsideofmain()–  Thismakesthestructuretypeavailabletoallcodethatfollowsthestructuredefinition(i.e.global)

•  TodeclaretwovariablesoftypeCDAccount:CDAccountmy_account,your_account;

my_accountandyour_accountcontaindistinctmembervariablesbalance,interest_rate,andterm

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SpecifyingMemberVariables•  Membervariablesarespecifictothestructurevariableinwhichtheyaredeclared

•  Syntaxtospecifyamembervariable(notethe‘.’) Structure_Variable_Name . Member_Variable_Name

•  Giventhedeclaration: CDAccountmy_account,your_account;

•  Usethedotoperatortospecifyamembervariable,e.g. my_account.balance isadouble my_account.interest_rate isadouble my_account.term isanint

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Notethestructdefinitionisplacedbeforemain()

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NotethedeclarationofCDAccount

Notethecalculationsdone

withthestructure’s

membervariables

Wearegoingto“fillin”thedatastructurethat’s“account”usingafunction…

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Notetheuseofthestructure’smembervariableswithaninputstream.

Notethatthestructureispassedintothefunctionascall-by-reference.

Youcanalsopassa

structurecall-by-value.

DuplicateNames

•  Membervariablenamesduplicatedbetweenstructuretypesarenotaproblem•  Thisisbecausewehavetousethedotoperator•  super_grow.quantityandapples.quantityaredifferentvariablesstoredin

differentlocationsincomputermemory

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structFertilizerStock{doublequantity;doublenitrogen_content;};FertilizerStocksuper_grow;

structCropYield{intquantity;doublesize;};CropYieldapples;

StructuresasReturnFunctionTypes

•  Structurescanalsobethetypeofavaluereturnedbyafunction

Example: CDAccountshrink_wrap (doublethe_balance,doublethe_rate,intthe_term)

{CDAccounttemp;temp.balance=the_balance;temp.interest_rate=the_rate;temp.term=the_term;returntemp;}

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Whatisthisfunctiondoing?

Example:UsingFunctionshrink_wrap

•  shrink_wrapbuildsacompletestructurevalueinthestructuretemp,whichisreturnedbythefunction

•  Wecanuseshrink_wraptogiveavariableoftypeCDAccountavalueinthisway:CDAccountnew_account;new_account=shrink_wrap(1000.00,5.1,11);

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AssignmentandStructures•  Theassignmentoperator(=)canalsobeusedtogivevaluestostructuretypes•  UsingtheCDAccountstructureagainforexample:

CDAccountmy_account,your_account;my_account.balance=1000.00;my_account.interest_rate=5.1;my_account.term=12;your_account=my_account;

•  Note:Thislastlineassignsallmembervariablesinyour_accountthecorrespondingvaluesinmy_account

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HierarchicalStructures

•  Structurescancontainmembervariablesthatarealsostructures

•  structPersonInfocontainsaDatestructure

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structDate{intmonth;intday;intyear;};

structPersonInfo{doubleheight;intweight;Datebirthday;};

UsingPersonInfoAnexampleon“.”operatoruse

•  AvariableoftypePersonInfoisdeclared:

PersonInfoperson1; •  Todisplaythebirthyearofperson1,

firstaccessthebirthdaymemberofperson1 cout<<person1.birthday…(wait!notcompleteyet!)

•  Butwewanttheyear,sowenowspecifytheyearmemberofthebirthdaymember cout<<person1.birthday.year;

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InitializingStructures

•  AstructurecanbeinitializedwhendeclaredExample: structDate {

intmonth; intday; intyear; };

•  Canbeinitializedinthisway–watchoutfortheorder!: Datedue_date={4,20,2018}; Date birthday={12,25,2000};

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monthdayyear

ApplicationofStructures

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LinkedLists!

PointersandLinkedLists

•  DefinitionofLinkedLists:Linearcollectionofdataelements,callednodes,eachpointingtothenextnodebymeansofapointer

•  Listelementscaneasilybeinsertedorremovedwithoutreorganizationoftheentirestructure(unlikearrays)

•  Dataitemsinalinkedlistdonothavetobestoredinonelargememoryblock(again,unlikearrays)

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LinkedLists

•  Youcanbuildalistof“nodes”whicharemadeupofvariablesandpointerstocreateachain.

•  Addinganddeletingnodesinthelinkcanbedoneby“re-routing”pointerlinks.

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Nodes

•  Theboxesinthepreviousdrawingrepresentthenodesofalinkedlist– Nodescontainthedataitem(s)andapointerthatcanpointtoanothernodeofthesametype

– Thepointerspointtoanentirenode,notanindividualitemthatmightbeinthenode

•  Thearrowsinthedrawingrepresentpointers

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NodesandPointers–AnIllustratedExample(shownasDisplay13.1inthetextbook)

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ImplementingNodes•  NodesareimplementedinC++asstructsorclasses•  Example:Astructuretostoretwodataitemsandapointertoanothernodeofthesametype,alongwithatypedefinitionmightbe: structListNode{ stringitem;intcount;ListNode*link;}; typedefListNode*ListNodePtr;

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This circular definition is allowed in C++

TheheadofaList

•  Theboxlabeledhead,inDisplay13.1,isnotanode,butsimplyapointervariablethatpointstoanode

•  Pointervariableheadisdeclaredas:ListNodePtrhead;

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structListNode{

stringitem;intcount;ListNode*link;};typedefListNode*ListNodePtr;ListNodePtrhead;

CreatingaLinkedList•  Firstcreatethenode(s)

ListNodemyNode1,myNode2; myNode1.item=“Thingamajiggie”; myNode1.count=5; //etc…

•  Thenlinktheheadpointertothe1stnodeinthelist

head=newListNode; *head=myNode1; //i.e.“whatheadlinkstoismyNode1”

•  Thenlinkalltheothernodestoeachother

*(myNode1.link)=myNode2;//etc…

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Checkoutdemo:linkedList.cpp

YOURTO-DOs

q TurninLab8onMondayq DoHW14byTuesday

q VisitTAs‘officehoursifyouneedhelp!q  Prof.willnothaveofficehoursnextMonday(Universityholiday)

q Enjoythelongweekend!J

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