Lecture 09 Oop 2010

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Introduction to ProgrammingEnvironments (C++/UNIX)

IPE 115, Semester 1, 2010

Lecture 09

Structures, OOP

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Structures

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INTRODUCTION TO PROGRAMMING ENVIROMENTS (C++/UNIX)

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Structures

A structure is a collection of variables

referenced under one name.

The variables that make up the structure are

called members, elements or fields.

Generally, all the members of a structure are

logically related.

Ex: a structure can contain information about a

persons name, address, age, height etc.

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Declaration of A Structure

struct car_part

{

int part_num;

char color;

double price;};

//To declare a variable of type car_part,

struct car_part partInfor;

Name of thestructure

Name of thevariable

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Accessing Members of A Structure

The . operator (dot operator) is used to access the structuremembers.

Values can be inserted into the members of the structure as,

partInfor.part_num = 100012;partInfor.color = r;

partInfor.priice = 4000.00;

Similarly, values can be read from the members of a structure

as,

int temp;

temp = partInfor.part_num;

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Abstract Data Types

We can develop new data types, which consist

of data elements and operations on those data

elements.

We describe these data types in a general

manner, which is not implementation

dependent.

In C++, we will use the Class feature to

implement our abstract data types.

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7/43INTRODUCTION TO PROGRAMMING ENVIROMENTS (C++/UNIX)

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C++ is a hybrid language

Up to now, we have dealt with C++ using theprocedural paradigm.

We break our problem into subtasks and implement thesubtasks using functions, building our main programfrom these functions.

C++ also allows us to build programs using theobject-oriented paradigm.

Also takes into account both code and data related toeach subtask/subgroup.

Organize these subgroups into a hierarchical structure

Translate these subgroups into self-contained units calledobjects.

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Object Oriented Programming

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Classes and Objects

A class is the abstract definition of the data

type. It includes the data elements that are part

of the data type, and the operations which are

defined on the data type.

An object is a specific instance of the data

type.

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Classes and Objects

An Object is an entity. It could be a realentity like a person a plane or somethingthat is imaginary.

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Classes and Objects

You can describe theentity by itsproperties and its

behaviors.

Plane

ModelAirLineNoOfPassengersFromTo

TakeOff

FlyLand

Properties

Methods

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Classes and Objects

A person working in a company

Person

EmpNoNameAddressBasicSal

OtHrsOtRate

CalcOtAmtCalcNetSal

Properties

Methods

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Classes and Objects

You describe the objectsdetails in a Class. Aclass is a blue print of anobject.

Blue PrintHouse3

House2

House1

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Objects

In C++ we have the data type integer and

various operations we can perform on integers.

However we do not get a specific instance of

an integer until we declare an integer variable.

Likewise to define a specific instance of a

class we declare an object (class variable).

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Defining and Instantiating Objects

class HouseHouse2

House1

House1, House2, House3 are objects.They are instances of the house class.

House House1, House2;In C++ you can also useHouse *House1 = new House()

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Properties are Private

Typically Properties are keptprivate. We use methods toaccess the value of theproperties.

e.g. setName, getName,

setEmpNo, getEmpNo

Person

EmpNoNameAddress

BasicSalOtHrsOtRate

CalcOtAmtCalcNetSal

Properties

Methods

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Using Objects

int main() {House myHouse;

myHouse.drawing(plan5.dwg);

myHouse.show();

return 0;

}

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Using Dynamic Objects

int main() {House *myHouse;

myHouse = new House();

myHouse->drawing(plan5.dwg);

myHouse->show();

delete myHouse;

return 0;

}

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Defining the class Rectangle

//class definitionclass Rectangle{private: //definition of data members

float length;

float width;public: //definition of operations

Rectangle(); //default constructorRectangle(int l, int w); //constructorfloat area();

float perimeter();void changeLength(int l);void changeWidth(int w);

}; //dont forget the semicolon

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Pictorial Representation of Class Rectangle

Rectangle

perimeter

area

changeLength

changeWidth

length

width

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Private and Public sections

The private part of the definition specifies thedata members of the class.

These are hidden from outside of the class and

can only be accessed through the operationsdefined for the class.

The public part of the definition specifies the

operations as function prototypes. These operations, or methods as they are

called, can be accessed by the main program.

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Defining the class Rectangle#include Rectangle.h

//class implementationRectangle::Rectangle() //constructor{

length = 0;width = 0;

}

Rectangle::Rectangle(int l, int w) //constructor{

length = l;width = w;

}

float Rectangle::area(){

return (length*width);}

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Defining the class Rectangle

float Rectangle::perimeter(){return (2*(length+width));

}

void Rectangle::changeLength(int l){

length = l;}

void Rectangle::changeWidth(int w){width = w;

}

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Some more information about constructors

Every class should have a constructor.

The constructor is used to initialize the object when itis declared.

The constructor does not return a value, and has noreturn type (not even void).

The constructor has the same name as the class.

Polymorphic1 constructors are allowed.

When an object is declared the appropriateconstructor is executed.

The default constructor has no parameters, and theobject is not followed by an argument list.

1. Polymorphism will be discussed formally in the next lecture

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Declaring And Using Objects

Objects are declared in a similar manner to thevariable of the built in types.

class_name object_name; or

class_name object_name(argument_list);

Eg: Rectangle House1;Rectangle House2 (28.5, 13.5);

To invoke a method on a particular object,

object_name.method_name(argument_list);Eg:

float floorSpace;

floorSpace = House.area();

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Clients

Programs that use classes and define objects

are called clients.

The only contact the client has with the private

data members of the object is through the

methods.

Client DataMembersmethods

class

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A Sample Client

Write a program which will determine the square

yardage to be mowed for a rectangular yard, given

the dimensions of the yard and the dimensions of the

house on that yard. It will also determine the cost ofmowing the lawn which is so much per square yard.

House

Yard

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Design Of Solution

Objects : Property //the entire yardHouse //the house

Strategy:

Input dimensions of property and house. Calculate area of property.

Calculate area of house.

Subtract area of house from area of property.

Input cost for mowing a square yard.

Determine the cost to mow the lawn.

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The Client Program

#include #include Rectangle.husing namespace std;int main(){

//length and width of rectanglefloat rlength, rwidth;

//Enter data for yardcout rlength >> rwidth;

//Define Yard objectRectangle Yard(rlength,rwidth);

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Client Program continued

//Enter data for house

cout rlength >> rwidth;

//Define House object

Rectangle House(rlength,rwidth);

//Declare variables for Area of House, Yard and Lawn.

float houseArea, yardArea, lawn;

//Compute Area of House and Yard using Area method.

houseArea = House.area();

yardArea = Yard.area();

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Client Program continued

//Compute Area of Lawn.lawn = yardArea houseArea;

//Input cost of mowing 1 square yard.

float mowCost;

cout > mowCost;

//Output cost of mowing lawn.

cout

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Separate Compilation

Generally the definition of a class is placed in afile, which is named by the class name and file

extension h.

Rectangle.h

The implementation is then placed in a file which

is named by the class name and file extension

cpp. This file must include the definition (.h) file.

Rectangle.cpp

The .cpp file can then be compiled by itself.

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Using Separately Compiled Files

Linux To compile Rectangle.cpp separately, type

- g++ Rectangle.cpp (this will generate an object file) andtype

- g++ -o prog prog.cpp Rectangle.o

- OR type g++ -o prog prog.cpp Rectangle.cpp

Visual C++

The main program is just one file in a project.

The main program should #include the .h files for anyclasses it is going to use.

The project should include the .h and .cpp files for theclasses that are going to be used.

Compile the main program, and then build the executable

file.

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Principles of Object-Oriented Design

Encapsulation

C++ uses classes for encapsulating a data type

Information Hiding

The use of private provide the hiding of the implementation of the data,

and protects it from use expect through the methods.

Polymorphism

The use of the same function name or operator in different ways based

on the arguments.

Inheritance

The ability to build a hierarchy of classes.

Dynamic Binding

The ability to determine which function to use at run-time.

h d f l d h

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When defining a class consider the

following types of methods

Constructors

Initialize objects when declared

Access methods

Return or output the value of a data member

Transformer methods

Modify a data member

Manipulator methods

Produce summary information about the object

Iterators

Allow you to move from one object to the next in a collection ofobjects

Destructors

Clean up when object goes out of scope.

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Polymorphism

Polymorphism occurs when a single function

name represents different tasks.

Operator overloading is, multiple

implementations of the actions of an operator,

where the particular implementation depends

on the types of the operators.

Also called, One Interface Multiple Methods

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Polymorphism

You can have multiple functions in a programwith the same function name provided theydiffer in either the number of parameters, or

the data type of the parameters. Two functions with the same name and the

same parameters (same number and type)cannot have same return types.

The compiler selects the appropriate functionby matching the arguments to the parameters.

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Example of Polymorphic Functions

#include

using namespace std;

int area(int side);int area(int length, int width);int area(double radius);

int main(){

cout

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Inheritance

Is a process by which one object can acquire

the properties of another object.

Supports the concept of classification.

Buildingroomsfloorsarea

Housebedroomsbaths

Schoolclassroomsoffices

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Base and Derived classes

The class that is inherited is referred to as a

base class. ( Building )

The class that does the inheriting is called the

derived class. ( House , School )

The derived class can also be used as a base

class by another derived class.

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How to inherit a class

Class derived_class_name : access base_class_name

{

//body of class

};

When one class inherits another, the membersof the base class become members of the

derived class.

The access status of the base class membersinside the derived class is determined by

access.

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Access

Class derived_class_name : access base_class_name{

//body of class

};

The access specifiers are:public,private andprotected. public:

- All public members of the base class become publicmembers of the derived class.

- All protected members of the base class become protectedmembers of the derived class.

- Bases private members remain private to the base

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Access (cont..)

Class derived_class_name : access base_class_name{

//body of class

};

The access specifiers are:public,private andprotected. private:

- All public and protected members of the base classbecome private members of the derived class.

protected:

- All public and protected members of the base classbecome protected members of the derived class.

Lecture 09 Oop 2010

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