Data Structure - CCVCLvisionlab.engr.ccny.cuny.edu/~fhu/Lecture04-05-Container.pdf · Data Structure -Section FG Lectures ... Data Structures and Other Objects Using C++ @Feng HU,

1@Feng HU, 2016@Feng HU, 2016

CSC212 Data Structure

- Section FG

Lectures4&5ContainerClasses

Instructor:FengHUDepartmentofComputerScience

CityCollegeofNewYork

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ContainerClasses

•Acontainerclassisadatatypethatiscapableofholdingacollectionofitems.

• InC++,containerclassescanbeimplementedasaclass,alongwithmemberfunctionstoadd,remove,andexamineitems.

Data Structuresand Other ObjectsUsing C++

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Bags

• Forthefirstexample,thinkaboutabag.

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Bags

• Forthefirstexample,thinkaboutabag.

• Insidethebagaresomenumbers.

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InitialStateofaBag

• Whenyoufirstbegintouseabag,thebagwillbeempty.

• Wecountonthistobetheinitialstate ofanybagthatweuse.

THIS BAGIS

EMPTY.

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InsertingNumbersintoaBag

• Numbersmaybeinsertedintoabag.

I AMPUTTING THE

NUMBER 4INTO THE

BAG.

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THE 4 ISIN THEBAG.

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• Thebagcanholdmanynumbers.

NOW I'MPUTTING

ANOTHERNUMBER IN THE BAG --

AN 8.

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THE 8 ISALSO IN

THE BAG.

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• Wecaneveninsertthesamenumbermorethanonce.

NOW I'MPUTTING ASECOND 4

IN THEBAG.

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• Wecaneveninsertthesamenumbermorethanonce.

NOW THEBAG HASTWO 4'S

AND AN 8..

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ExaminingaBag

• Wemayaskaboutthecontentsofthebag.

HAVEYOU GOTANY 4's

?

YES,I HAVETWO OFTHEM.

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RemovingaNumberfromaBag

• Wemayremoveanumberfromabag.

THIS4 IS

OUTTAHERE!

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RemovingaNumberfromaBag

• Wemayremoveanumberfromabag.

• Butweremoveonlyonenumberatatime. ONE 4 IS

GONE, BUTTHE OTHER4 REMAINS.

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HowManyNumbers

• Anotheroperationistodeterminehowmanynumbersareinabag. IN MY OPINION,

THERE ARE TOO MANY NUMBERS.

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SummaryoftheBagOperations

➊Abagcanbeputinitsinitial state,whichisanemptybag.➋Numberscanbeinserted intothebag.➌Youmaycount howmanyoccurrenceofacertainnumberareinthebag.❹Numberscanbeerased fromthebag.❺Youcancheckthesize ofthebag(i.e.howmanynumbersareinthebag).

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Thebag Class

• C++classes(introducedinChapter2)canbeusedtoimplementacontainerclasssuchasabag.

• Theclassdefinitionincludes:

class bag

✔ The heading of the definition

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Thebag Class

• C++classes(introducedinChapter2)canbeusedtoimplementacontainerclasssuchasabag.

• Theclassdefinitionincludes:

class bag{public:

bag( );

✔ The heading of the definition✔A constructor prototype

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The bag Class

❐ C++ classes (introduced in Chapter 2) can be used to implement a container class such as a bag.

❐ The class definition includes:

class bag{public:

bag( );void insert(...void erase(......and so on✔ The heading of the definition

✔A constructor prototype✔ Prototypes for public

member functions

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The bag Class

❐ C++ classes (introduced in Chapter 2) can be used to implement a container class such as a bag.

❐ The class definition includes:

class bag{public:

bag( );void insert(...void erase(......and so on

private:

};

✔ The heading of the definition✔A constructor prototype✔ Prototypes for public

member functions✔ Private member variables

We’ll look at privatemembers later.

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Thebag’sDefaultConstructor

• Placesabagintheinitialstate(anemptybag)

bag::bag( )// Postcondition: The bag has been initialized// and it is now empty. {. . .

}

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Theinsert Function

• Insertsanewnumberinthebag

void bag::insert(const int& new_entry)// Precondition: The bag is not full.// Postcondition: A new copy of new_entry has // been added to the bag.{

. . .}

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Thesize Function

• Checkshowmanyintegersareinthebag.

int bag::size( ) const// Postcondition: The return value is the number// of integers in the bag.{

. . .}

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Thesize Function

• Checkshowmanyintegersareinthebag.

size_t bag::size( ) const// Postcondition: The return value is the number// of integers in the bag.{

. . .}

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Thecount Function

• Countshowmanycopiesofanumberoccur

size_t bag::count(const int& target) const// Postcondition: The return value is the number// of copies of target in the bag.{

. . .}

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Theerase_one Function

• Removes(erase)onecopyofanumber

void bag::erase_one(const int& target)// Postcondition: If target was in the bag, then// one copy of target has been removed from the// bag; otherwise the bag is unchanged.{

. . .}

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TheHeaderFileandImplementationFile

• Theprogrammerwhowritesthenewbagclassmustwritetwofiles:

• bag1.h,aheaderfilethatcontainsdocumentationandtheclassdefinition

• bag1.cxx,animplementationfilethatcontainstheimplementationsofthebag ’smemberfunctions

bag’s documentation

bag’s class definition

Implementations of thebag’s member functions

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Documentationforthebag Class

• Thedocumentationgivesprototypesandspecifications forthebagmemberfunctions.

• Specificationsarewrittenasprecondition/postcondition contracts.

• Everythingneededtouse thebag classisincludedinthiscomment.




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Thebag ’sClassDefinition

• Afterthedocumentation,theheaderfilehastheclassdefinitionthatwe’veseenbefore:




class bag{public:

bag( );void insert(...void erase(......and so on

private:…};

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TheImplementationFile

• Aswithanyclass,theactualdefinitionsofthememberfunctionsareplacedinaseparateimplementationfile.

• Theimplementationsofthebag’smemberfunctionsareinbag1.cxx.




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AQuiz

① YesIcan.② No.NotunlessIseetheclass

definitionforthebag .③ No.Ineedtoseetheclass

definitionforthebag ,andalsoseetheimplementationfile.

Suppose that a Mysterious Benefactor provides you with the bag class, but you are only permitted to read the documentation in the header file. You cannot read the class definition or implementation file. Can you write a program that uses the bag data type ?

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AQuiz

① YesIcan.Youknowthenameofthenewdatatype,whichisenoughforyoutodeclarebag variables.Youalsoknowtheheadingsandspecificationsofeachoftheoperations.

Suppose that a Mysterious Benefactor provides you with the Bag class, but you are only permitted to read the documentation in the header file. You cannot read the class definition or implementation file. Can you write a program that uses the bag data type ?

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Usingthebag inaProgram

• Hereistypicalcodefromaprogramthatusesthenewbag class:

bag ages;

// Record the ages of three children:ages.insert(4);ages.insert(8);ages.insert(4);

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ImplementationDetails

• Theentriesofabagwillbestoredinthefrontpartofanarray,asshowninthisexample.

[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . . .

An array of integers

4 8 4

We don't care what's inthis part of the array.

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• Theentriesmayappearinanyorder.Thisrepresents thesamebagasthepreviousone...


4 4 8


[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . . .

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• ...andthisalsorepresentsthesamebag.

An array of integersWe don't care what's in

this part of the array.

[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . . .

8 4 4

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• Wealsoneedtokeeptrackofhowmanynumbersareinthebag.


8 4 4


An integer to keeptrack of the bag's size

3

[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . . .

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AnExercise

Use these ideas to write a list of private member variables could implement the bag class. You should have two member variables. Make the bag capable of holding up to 20 integers.

You have 60 secondsto write the declaration.

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AnExercise

class bag{public:

...private:

int data[20];size_t used;

};

One solution:

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AnExercise

A more flexible solution:

class bag{public:

static const size_t CAPACITY = 20;...

private:int data[CAPACITY];size_t used;

};

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TheInvariantofaClass

• Tworulesforourbagimplementation• Thenumberofitemsinthebagisstoredinthemembervariableused;

• Foranemptybag,wedon’tcarewhatisstoredinanyofdata;foranon-emptybag,theitemsarestoredindata[0]throughdata[used-1], andwedon’tcarewhatarestoredintherestofdata.

• Therulesthatdictatehowthemembervariablesofa(bag)classareusedtorepresentavalue(suchasabagofitems)arecalledtheinvariant of the class

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• Theinvariant of the class isessentialtothecorrectimplementationoftheclass’sfunctions

• Insomesense,• theinvariantofaclassisacondition thatisanimplicit partofeveryfunction’s postcondition

• And (exceptfortheconstructors)itisalsoanimplicit partofeveryfunction’sprecondition.

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• PreconditionandPostcondition• contractforeachfunction,foruseofthefunction• documentpre- andpost- intheheaderfile

• Theinvariant of the class • implicit partofpre- andpost- soisnotusuallywrittenasanexplicit partofpre- andpost-

• abouttheprivatemembervariables,thusforimplementation,butnotforhowtousethem

• documentedintheimplementationfile•ValueSemantics

• bothforimplementationandforuse• documentedintheheaderfile

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AnExampleofCallinginsert

void bag::insert(const int& new_entry)

Before calling insert, wemight have this bag b:

2

[ 0 ] [ 1 ] [2] . . .

8 4b.data

b.used

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void Bag::insert(int new_entry)

b.data

b.used

We make a function callb.insert(17)

What values will be inb.data and b.countafter the member function finishes ?

2

[ 0 ] [ 1 ] [2] . . .

8 4


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void Bag::insert(int new_entry)

After calling b.insert(17),we will have this bag b:

3

[ 0 ] [1] [ 2 ] . . .

8 4 17


b.data

b.used2

[ 0 ] [ 1 ] [2] . . .

8 4

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Pseudocodeforbag::insert

➊ assert(size( ) < CAPACITY);➋ Placenew_entry intheappropriatelocationofthedata

array.

➌ Addonetothemembervariablecount.

What is the “appropriatelocation” of the data array ?

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array.


data[used] = new_entry;used++;

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array.


data[ used++] = new_entry;

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Summary

•Acontainerclassisaclassthatcanholdacollectionofitems.

•ContainerclassescanbeimplementedwithaC++class.

• Theclassisimplementedwith• aheaderfile(containingdocumentationandtheclassdefinition)bag1.h and

• animplementationfile(containingtheimplementationsofthememberfunctions)bag1.cxx.

•OtherdetailsaregiveninSection3.1,whichyoushouldread,especiallytherealbagcode

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OutlineforLecture5

•Bagclassdefinition/implementationdetails• Inlinefunctions

• constructor,size• Otherbasicfunctions

• insert,erase_one,erase,count• Moreadvancedfunctions

• operators+,+=,-

• TimeAnalysis• Big-O

• Introductiontosequence

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TheOtherbag Operations

•ReadSection3.1fortheimplementationsoftheotherbagmemberfunctions• suchasoperatorsappend (+=)andunion (+)

•Remember:Ifyouarejustusing thebag class• thenyoudon’tneedtoknowhowtheoperationsareimplemented.

• Laterwewillreimplement thebagusingmoreefficienttechniques.

•We’llalsohaveafewotheroperationstomanipulatebags.

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AppendOperator+=

void bag::operator+=(const bag& addend)// Precondition: size( ) + addend.size( ) <= CAPACITY.// Postcondition: Each item in addend has been added to this bag.

{size_t i;assert(size( ) + addend.size( ) <= CAPACITY);for (i = 0; i< addend.used; ++i){

data[used] = addend.data[i];++used;

}}

// calling program: a += b; (OKAY)// Question : What will happen if you call: b += b;

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AppendOperator+=

void bag::operator+=(const bag& addend)// Precondition: size( ) + addend.size( ) <= CAPACITY.// Postcondition: Each item in addend has been added to this bag.// Library facilities used: algorithm, cassert{

assert(size( ) + addend.size( ) <= CAPACITY);

copy(addend.data, addend.data + addend.used, data + used);used += addend.used;

}

// copy (<beginning location>, ending location>, <destination>);// Question : Can you fix the bug in the previous slide without using copy ?

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UnionOperator+

// NONMEMBER FUNCTION for the bag class:bag operator+(const bag& b1, const bag& b2)// Precondition: b1.size( ) + b2.size( ) <= bag::CAPACITY.// Postcondition: The bag returned is the union of b1 and b2.// Library facilities used: cassert{

bag answer;

assert(b1.size( ) + b2.size( ) <= bag::CAPACITY);

answer += b1; answer += b2;return answer;

}

// calling program: c =a+b; // Question : what happens if you call a =a+b ?

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SubtractOperator-

// Prototype: NONMEMBER friend FUNCTION for the bag class:// bag operator-(const bag& b1, const bag& b2);// Postcondition: For two bags b1 and b2, the bag x-y contains all the

items of x, with any items from y removed// Write your implementation// HINTS:// 1. A friend function can access private member variables of a bag// 2. You cannot change constant reference parameters// 3. You may use any member functions of the bag class such as// b1.count(target); // how many target is in bag b1?// b1.erase_one(target); // target is an integer item// b2.size(); // size of the bag b2;// bag b3(b2); // automatic copy constructor//

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SubtractOperator-

// NONMEMBER friend FUNCTION for the bag class:bag operator-(const bag& b1, const bag& b2)// Postcondition: For two bags b1 and b2, the bag x-y contains all the

items of x, with any items from y removed{

size_t index;bag answer(b1); // copy constructorsize_t size2 = b2.size(); // use member function sizefor (index = 0; index < size2; ++index){

int target = b2.data[index]; // use private member variableif (answer.count(target) ) // use function count

answer.erase_one(target); // use function erase_one}return answer;

}

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OtherKindsofBags

• Inthisexample,wehaveimplementedabagcontainingintegers.• Butwecouldhavehadabagoffloatnumbers,abagofcharacters,abagofstrings ...

Suppose you wanted one of these other bags. How much would you need to change in the implementation ?Section 3.1 gives a simple solution usingthe C++ typedef statement.

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TimeAnalysisoftheBagClass

• count– thenumberofoccurrence• erase_one– removeonefromthebag• erase– removeall• +=- append• b1+b2- union• insert– addoneitem• size– numberofitemsinthebag

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What’sthemostimportant,then?

•ConceptofContainerClasses• thebagclassisnotparticularlyimportant

•Otherkindsofcontainerclasses• sequence – similartoabag,bothcontainabunchofitems.Butunlikeabag,theitemsinasequenceisarrangedinorder.

• willbethetopicofoursecondassignment– payingattentiontothedifferences

• index– havecurrent,next,last,etc• memberfunctionsandtheirimplementation(e.g.insert,attach)• timeanalysis(insert)

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AfterClass…

• Assignment2• DueWednesday,Sept28• Reading:Chapter3,Section3.2-3.3• especiallythesequencecode

• Self-TestExercises• 1,3,5,10,11,14,18-24

• Readingfornextlecture• Chapter4,Section4.1-4.2

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Summary

•Acontainerclassisaclassthatcanholdacollectionofitems.

•ContainerclassescanbeimplementedwithaC++class.

• Theclassisimplementedwith• aheaderfile(containingdocumentationandtheclassdefinition)bag1.h and

• animplementationfile(containingtheimplementationsofthememberfunctions)bag1.cxx.

•OtherdetailsaregiveninSection3.1,whichyoushouldread,especiallytherealbagcode

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THE END

Presentation copyright 1997, Addison Wesley LongmanFor use with Data Structures and Other Objects Using C++by Michael Main and Walter Savitch.

Some artwork in the presentation is used with permission from Presentation Task Force(copyright New Vision Technologies Inc.) and Corel Gallery Clipart Catalog (copyrightCorel Corporation, 3G Graphics Inc., Archive Arts, Cartesia Software, Image ClubGraphics Inc., One Mile Up Inc., TechPool Studios, Totem Graphics Inc.).

Students and instructors who use Data Structures and Other Objects Using C++ arewelcome to use this presentation however they see fit, so long as this copyright notice remains intact.

This lecture was modified from the authors’ presentation, with new conventions provided in the second edition (2001) of the textbook and other minor changes -- Feng HU, 2016, CCNY

Documents

Data Structure - CCVCLvisionlab.engr.ccny.cuny.edu/~fhu/Lecture04-05-Container.pdf · Data Structure -Section FG Lectures ... Data Structures and Other Objects Using C++ @Feng HU,