CSC335-Chapter4

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(Chapter 4More about OOP and ADTsClasses)

CSC-335

Data Structures and Algorithms

Instructor:Ahmad Reza Hadaegh

The content of this power point lecture has been originallycreated by Christos Kolonis and modified by

Dr. Ahmad R. Hadaegh

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Chapter Contents

4.1 Procedural vs. Object-Oriented Programming

4.2 Classes

4.3 Example: A First Version of a User-Defined

Time Class

4.4 Class Constructors

4.5 Other Class Operators

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Chapter Objectives

Contrast OOP with procedural programming Review classes in C++

Study in detail a specific example of how a class is built

Show how operators can be overloaded for new types

Show how conditional compilation directives are used toavoid redundant declarations

Discuss pointers to class objectsthe thispointer, inparticular

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4.1 Contrast Procedural, Object Oriented Paradigms

ProceduralAction-oriented concentrates

on the verbs

Programmers:

Identify basic tasks to solve

problem Implement actions to do tasks as

subprograms (procedures /functions / subroutines)

Group subprograms intoprograms / modules / libraries,

together make up a completesystem for solving the problem

Object-oriented Focuses on the nounsof problem

specification

Programmers:

Determine objects needed for

problem Determine how they should work

together to solve the problem.

Create types called classes madeup of

data members

function membersto operate onthe data.

Instances of a type (class) calledobjects.

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4.2 Structs and ClassesSimilarities

Essentially the same syntax Both are used to model objects with multiple

attributes (characteristics)

represented as data members

also called fields or

instance or attribute variables).

Thus, both are used to process non-

homogeneous data sets.

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Structs vs. ClassesDifferences

No classes in C

Members public by default

Can be specified private

Both structs and classesin C++

Structs can havemembers declared private

Class members areprivate by default

Can be specified public

Structs (in C) Classes & Classes (in C++)

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Advantages in C++(structs and Classes)

C++ structs and classes model objects whichhave:

Attributes represented as data members

Operations represented as functions (or methods) Leads to object oriented programming

Objects are self contained

"I can do it myself" mentality

They do not pass a parameter to an external function

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Class Declaration

Syntax

class ClassName{

public:

Declarations of public membersprivate:Declarations of private members

};

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Designing a Class

Data members normally placed in private: sectionof a class

Function members usually in public: section

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Class Libraries

Class declarations placed in header file Given .hextension

Contains data items and prototypes

Implementation file

Same prefix name as header file

Given .cppextension

Programs which use this class library called client

programs

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Translating a Library

Fig. 4.1

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4.3 Example of User-DefinedTimeClass

Recall Time struct from previous chapter Actions done to Timeobject required use of Timeparameter in

the functions

Now we create a Time class

Actions done to Timeobject, done by the object itself

Data members privateinaccessible to users of the class

Information hiding

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4.4 Constructors

Constructor definition in Time.cpp example

Syntax

ClassName::ClassName (parameter_list): member_initializer_list{

// body of constructor definition}

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4.4 Constructors

Results of defaultconstructor

Results of explicit-valueconstructor

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Overloading Functions

Note existence of multiple functions with the

same name:

Time();Time(unsigned initHours,

unsigned initMinutes,char initAMPM);

Known as overloading

Compiler compares numbers and types ofarguments of overloaded functions

Checks the "signature" of the functions

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ConstructorFunmction Overloadingrefers to Figure 4.7 in the book

Class Time

{

public:

Time();

Time(unsigned initHours, unsigned initMinutes, char initAMPM

void Display(ostream& out) const;

void read(istream& in);

private:

unsigned myHours; myMinutes;

char myAMorPM;

unsigned myMilTime // military time equivalent

};

Having multiple constructor is a sign of function overloading. Functionoverloading refers to multiple functions with the same name butdifferent signature (number of parameters may be different. Type ofparameters can be different too).

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Default Arguments

Possible to specify default values for constructor

argumentsTime(unsigned initHours = 12,

unsigned initMinutes = 0,

char initAMPM = 'A');

ConsiderTime t1, t2(5), t3(5,30), t4(5,30,'P');

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Section 4.5 - Other Class Operations

Accessors and Mutators See get and set functions

Overloading operators

Same symbol can be used more than one way

Note declaration for I/O operators >

Note definitionof overloaded I/O operators

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Copy Operations We can assign one object to another. For example suppose object

bedTime and midnight have been created. For the followingassignments statement, we have :

Time t = bedTime

Or t = midnight;

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Friend Functions

Note use of two functions used for output display() andoperator

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Friend Functions

Implementation of the function

ostream & operator

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Redundant Declarations

Note use of #include "Time.h" in Time.cpp

Client program

Causes "redeclaration" errors at compile time

Solution is to use conditional compilation

Use #ifndef and #define and #endif compiler directives

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Pointers to Class Objects

Possible to declare pointers to class objectsTime * timePtr = &t;

Access withtimePtr->getMilTime() or(*timePtr).getMilTime()

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The thisPointer

Every class has a keyword, this

a pointer whose value is the address of the object Value of *thiswould be the object itself