1 CSC212 Data Structure - Section RS Lectures 4 & 5 Container Classes Instructor: Zhigang Zhu...

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CSC212 Data Structure - Section RS

CSC212 Data Structure - Section RS

Lectures 4 & 5Lectures 4 & 5

Container ClassesContainer Classes

Instructor: Zhigang ZhuInstructor: Zhigang Zhu

Department of Computer Science Department of Computer Science

City College of New YorkCity College of New York

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A A container class container class is a data is a data type that is capable of type that is capable of holding a collection of holding a collection of items.items.

In C++, container classes In C++, container classes can be implemented as a can be implemented as a class, along with member class, along with member functions to add, remove, functions to add, remove, and examine items.and examine items.

Container ClassesContainer Classes

Data StructuresData Structuresand Other Objectsand Other ObjectsUsing C++Using C++

33

BagsBags

For the first example, For the first example, think about a bag.think about a bag.

44

BagsBags

For the first example, For the first example, think about a bag.think about a bag.

Inside the bag are Inside the bag are some numbers.some numbers.

55

Initial State of a BagInitial State of a Bag

When you first begin When you first begin to use a bag, the bag to use a bag, the bag will be empty.will be empty.

We count on this to be We count on this to be the the initial stateinitial state of any of any bag that we use.bag that we use.

THIS BAGIS

EMPTY.

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Inserting Numbers into a BagInserting Numbers into a Bag

Numbers may be Numbers may be inserted into a bag.inserted into a bag.

I AMPUTTING THE

NUMBER 4INTO THE

BAG.

77



THE 4 ISIN THEBAG.

88



The bag can hold The bag can hold many numbers.many numbers.

NOW I'MPUTTINGANOTHER

NUMBER IN THE BAG --

AN 8.

99




THE 8 ISALSO IN

THE BAG.

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We can even insert We can even insert the same number the same number more than once.more than once. NOW I'M

PUTTING ASECOND 4

IN THEBAG.

1111




We can even insert We can even insert the same number the same number more than once.more than once.

NOW THEBAG HASTWO 4'S

AND AN 8..

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Examining a BagExamining a Bag

We may ask about We may ask about the contents of the the contents of the bag. bag.

HAVEYOU GOTANY 4's

?

YES,I HAVETWO OFTHEM.

1313

Removing a Number from a BagRemoving a Number from a Bag

We may remove a We may remove a number from a bag. number from a bag.

THIS4 IS

OUTTAHERE!

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Removing a Number from a BagRemoving a Number from a Bag

We may remove a We may remove a number from a bag.number from a bag.

But we remove only But we remove only one number at a one number at a time. time.

ONE 4 ISGONE, BUTTHE OTHER4 REMAINS.

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How Many NumbersHow Many Numbers

Another operation is Another operation is to determine how to determine how many numbers are in a many numbers are in a bag.bag.

IN MY OPINION, THERE ARE TOO MANY NUMBERS.

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Summary of the Bag OperationsSummary of the Bag Operations

A bag can be put in its A bag can be put in its initial stateinitial state, , which is an empty bag.which is an empty bag.

Numbers can be Numbers can be insertedinserted into the bag. into the bag. You may You may countcount how many occurrence of how many occurrence of

a certain number are in the bag.a certain number are in the bag. Numbers can be Numbers can be erasederased from the bag. from the bag. You can check the You can check the sizesize of the bag (i.e. of the bag (i.e.

how many numbers are in the bag).how many numbers are in the bag).

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The bag ClassThe bag Class

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

The class definition includes:The class definition includes:

class bag

The heading of the definition

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


class bag{public: bag( );

The heading of the definition A constructor prototype

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


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


class bag{public: bag( ); void insert(... void erase(... ...and so onprivate:

};

The heading of the definition A constructor prototype Prototypes for public member functions Private member variables

We’ll look at privatemembers later.

We’ll look at privatemembers later.

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The bag’s Default ConstructorThe bag’s Default Constructor

Places a bag in the initial state (an empty Places a bag in the initial state (an empty bag)bag)

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

}

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The insert FunctionThe insert Function

Inserts a new number in the bagInserts a new number in the bag

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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The size FunctionThe size Function

Checks how many integers are in the bag.Checks how many integers are in the bag.

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

. . .}

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The size FunctionThe size Function

Checks how many integers are in the bag.Checks how many integers are in the bag.

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

. . .}

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The count FunctionThe count Function

Counts how many copies of a number occurCounts how many copies of a number occur

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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The erase_one FunctionThe erase_one Function

Removes (erase) one copy of a numberRemoves (erase) one copy of a number

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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The Header File and Implementation FileThe Header File and Implementation File

The programmer who writes The programmer who writes the new the new bagbag class must write class must write two files:two files:

bag1.hbag1.h, a header file that , a header file that contains documentation and contains documentation and the class definitionthe class definition

bag1.cxxbag1.cxx, an implementation , an implementation file that contains the file that contains the implementations of the implementations of the bagbag ’s ’s member functionsmember functions

bag’s documentation

bag’s class definition

Implementations of thebag’s member functions

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Documentation for the bag ClassDocumentation for the bag Class

The documentation gives The documentation gives prototypes and prototypes and specificationsspecifications for the bag for the bag member functions.member functions.

Specifications are written as Specifications are written as precondition/postcondition precondition/postcondition contracts.contracts.

Everything needed to Everything needed to useuse the the bagbag class is included in this class is included in this comment.comment.




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The bag ’s Class DefinitionThe bag ’s Class Definition

After the documentation, After the documentation, the header file has the class the header file has the class definition that we’ve seen definition that we’ve seen before:before:




class bag{public: bag( ); void insert(... void erase(... ...and so onprivate:…};

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The Implementation FileThe Implementation File

As with any class, the As with any class, the actual definitions of the actual definitions of the member functions are member functions are placed in a separate placed in a separate implementation file.implementation file.

The The implementations implementations of of the the bagbag’s member ’s member functions are in functions are in bag1.cxxbag1.cxx..




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A QuizA Quiz

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

Yes I can.Yes I can.No. Not unless I see the No. Not unless I see the

class definition for the class definition for the bagbag ..

No. I need to see the No. I need to see the class definition for the class definition for the bagbag , and also see the , and also see the implementation file.implementation file.

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A QuizA Quiz

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

Yes I can.Yes I can.

You know the name of the You know the name of the new data type, which is new data type, which is enough for you to declare enough for you to declare bagbag variables. You also variables. You also know the headings and know the headings and specifications of each of specifications of each of the operations.the operations.

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Using the bag in a ProgramUsing the bag in a Program

Here is typical code from a Here is typical code from a program that uses the new program that uses the new bagbag class: class:

bag ages;

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

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Implementation DetailsImplementation Details

The entries of a bag The entries of a bag will be stored in the will be stored in the front part of an array, front part of an array, as shown in this as shown in this example. example.

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

An array of integersAn array of integers

4 8 4

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

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The entries may The entries may appear in any order. appear in any order. This represents the This represents the same bag as the same bag as the previous one. . . previous one. . .


4 4 8


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

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. . . and this also . . . and this also represents the same represents the same bag.bag.

An array of integersAn array of integersWe don't care what's inWe don't care what's inthis part of the array.this part of the array.

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

8 4 4

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We also need to keep track of how We also need to keep track of how many numbers are in the bag.many numbers are in the bag.


8 4 4


An integer to keepAn integer to keeptrack of the bag's sizetrack of the bag's size

3

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

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An ExerciseAn Exercise

Use these ideas to write a Use these ideas to write a list of private member list of private member variables could implement variables could implement

the the bagbag class. You class. You should have two member should have two member variables. Make the bag variables. Make the bag capable of holding up to capable of holding up to 20 integers.20 integers.

You have 60 secondsto write the declaration.

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class bag{public: ...private: int data[20]; size_t used;};

One solution:One solution:

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A more flexible solution:A more flexible solution:

class bag{public: static const size_t CAPACITY = 20; ...private: int data[CAPACITY]; size_t used;};

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The Invariant of a ClassThe Invariant of a Class

Two rules for our bag implementationTwo rules for our bag implementation The number of items in the bag is stored in the The number of items in the bag is stored in the

member variable member variable usedused;; For an empty bag, we don’t care what is stored in any For an empty bag, we don’t care what is stored in any

of of datadata; for a non-empty bag, the items are stored in ; for a non-empty bag, the items are stored in datadata[0] through [0] through datadata[[usedused-1], and we don’t care what -1], and we don’t care what are stored in the rest of are stored in the rest of datadata..

The rules that dictate how the member variables The rules that dictate how the member variables of a (bag) class are used to represent a value (such of a (bag) class are used to represent a value (such as a bag of items) are called the as a bag of items) are called the invariant of the invariant of the classclass

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The The invariant of the class invariant of the class is essential to is essential to the correct implementation of the class’s the correct implementation of the class’s functionsfunctions

In some sense, In some sense, the invariant of a class is a condition that is an the invariant of a class is a condition that is an implicitimplicit part of every function’s postcondition part of every function’s postcondition

And (except for the constructors) it is also an And (except for the constructors) it is also an implicitimplicit part of every function’s precondition. part of every function’s precondition.

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Precondition and PostconditionPrecondition and Postcondition contract for each function, for use of the functioncontract for each function, for use of the function document pre- and post- in the header filedocument pre- and post- in the header file

The The invariant of the class invariant of the class implicitimplicit part of pre- and post- so is not usually written as part of pre- and post- so is not usually written as

an an explicitexplicit part of pre- and post- part of pre- and post- about the private member variables, thus for about the private member variables, thus for

implementation, but not for how to use themimplementation, but not for how to use them documented in the implementation filedocumented in the implementation file

Value SemanticsValue Semantics both for implementation and for useboth for implementation and for use documented in the header filedocumented in the header file

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An Example of Calling insertAn Example of Calling insert

void bag::insert(const int& new_entry)

Before calling insert, weBefore calling insert, wemight have this bag b:might have this bag b:

2

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

8 4b.datab.data

b.usedb.used

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void Bag::insert(int new_entry)

b.datab.data

b.usedb.used

We make a function callWe make a function callb.insert(17)b.insert(17)

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

2

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

8 4


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void Bag::insert(int new_entry)

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

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

8 4 1717


b.datab.data

b.usedb.used2

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

8 4

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Pseudocode for bag::insertPseudocode for bag::insert

assert(size( ) < CAPACITY);assert(size( ) < CAPACITY);

Place Place new_entrynew_entry in the appropriate location in the appropriate location of the of the datadata array. array.

Add one to the member variable Add one to the member variable countcount..

What is the “appropriatelocation” of the data array ?

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data[used] = new_entry;used++;

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data[ used++] = new_entry;

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A container class is a class that can hold a collection A container class is a class that can hold a collection of items.of items.

Container classes can be implemented with a C++ Container classes can be implemented with a C++ class.class.

The class is implemented with The class is implemented with a header file (containing documentation and the class a header file (containing documentation and the class

definition) definition) bag1.hbag1.h and and an implementation file (containing the implementations of an implementation file (containing the implementations of

the member functions) the member functions) bag1.cxxbag1.cxx.. Other details are given in Section 3.1, which you Other details are given in Section 3.1, which you

should read, especially the real should read, especially the real bag codebag code

Summary Summary

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Outline for Lecture 5Outline for Lecture 5

Bag class definition/implementation detailsBag class definition/implementation details Inline functionsInline functions

constructor, sizeconstructor, size Other basic functions Other basic functions

insert, erase_one, erase, countinsert, erase_one, erase, count More advanced functions More advanced functions

operators +, +=, -operators +, +=, -

Time Analysis Time Analysis Big-O Big-O

Introduction to sequence Introduction to sequence

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Summary Summary

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The Other bag OperationsThe Other bag Operations

Read Section 3.1 for the implementations of the Read Section 3.1 for the implementations of the other bag member functionsother bag member functions such as operators such as operators appendappend (+=) and (+=) and unionunion (+) (+)

Remember: If you are just Remember: If you are just usingusing the the bagbag class class then you don’t need to know how the operations are then you don’t need to know how the operations are

implemented.implemented. Later we will Later we will reimplementreimplement the bag using more the bag using more

efficient techniques. efficient techniques. We’ll also have a few other operations to We’ll also have a few other operations to

manipulate bags.manipulate bags.

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Append Operator +=Append Operator +=

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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Append Operator +=Append Operator +=

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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Union Operator +Union Operator +

// 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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Subtract Operator -Subtract Operator -

// 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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Subtract Operator -Subtract Operator -

// 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 size for (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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Other Kinds of BagsOther Kinds of Bags

In this example, we have implemented a In this example, we have implemented a bag containing bag containing integersintegers..

But we could have had a bag of But we could have had a bag of float float numbersnumbers, a bag of , a bag of characterscharacters, a bag of , a bag of stringsstrings . . . . . .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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Time Analysis of the Bag ClassTime Analysis of the Bag Class

count – the number of occurrencecount – the number of occurrence erase_one – remove one from the bagerase_one – remove one from the bag erase – remove all erase – remove all += - append+= - append b1+b2 - unionb1+b2 - union insert – add one item insert – add one item size – number of items in the bagsize – number of items in the bag

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What’s the most important, then?What’s the most important, then?

Concept of Container ClassesConcept of Container Classes the bag class is not particularly importantthe bag class is not particularly important

Other kinds of container classesOther kinds of container classes sequencesequence – similar to a bag, both contain a bunch of – similar to a bag, both contain a bunch of

items. But unlike a bag, the items in a sequence is items. But unlike a bag, the items in a sequence is arranged in order.arranged in order.

will be the topic of our will be the topic of our second assignmentsecond assignment– paying – paying attention to the differences attention to the differences

index – have current, next, last, etcindex – have current, next, last, etc member functions and their implementation (e.g. insert, attach)member functions and their implementation (e.g. insert, attach) time analysis (insert)time analysis (insert)

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After Class…After Class…

Assignment 2 (online now)Assignment 2 (online now) Due Thursday, Feb 25Due Thursday, Feb 25 Reading: Chapter 3, Section 3.2-3.3Reading: Chapter 3, Section 3.2-3.3 especially the especially the sequence codesequence code

Self-Test ExercisesSelf-Test Exercises 1,3, 5,10,11,14,18-241,3, 5,10,11,14,18-24

Reading for next lecture Reading for next lecture Chapter 4, Section 4.1-4.2Chapter 4, Section 4.1-4.2

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Summary Summary

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THE ENDTHE END

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

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

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

This lecture was modified from the authors’ presentation, with new This lecture was modified from the authors’ presentation, with new conventions provided in the second edition (2001) of the textbook and conventions provided in the second edition (2001) of the textbook and other minor changes -- Z. Zhu, 2002-2010, CCNYother minor changes -- Z. Zhu, 2002-2010, CCNY

1 CSC212 Data Structure - Section RS Lectures 4 & 5 Container Classes Instructor: Zhigang Zhu...

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