C++ppt. Classs and object, class and object

Introduction
• Object-oriented programming (OOP)
– Encapsulation: encapsulates data (attributes) and
functions (behaviour) into packages called classes
– Information hiding : implementation details are hidden
within the classes themselves
• Classes
– Classes are the standard unit of programming
– Aclass is like a blueprint – reusable
– Objects are instantiated (created) from the class
– For example, a house is an instance of a “blueprint
class”

Implementing a Time Abstract Data Type
with a Class
• Classes
– Model objects that have attributes (data
members) and behaviours (member functions)
– Defined using keyword class
– Have a body delineated with braces ({ and })
– Class definitions terminate with a semicolon
– Example:

1 class Time {
2 public:
3 Time();
4 void setTime( int, int, int );
5 void printMilitary();
6 void printStandard();
7 private:
Public: and Private: are
member-access specifiers.
setTime, printMilitary, and
printStandard are member
functions.
Time is the constructor.
8 int hour; // 0 - 23
9 int minute; // 0 - 59
10 int second; // 0 - 59 hour, minute, and second
11 }; are data members.

Implementing a Time Abstract Data Type
with a Class
• Member access specifiers
– Classes can limit the access to their member functions and data
– The three types of access a class can grant are:
• Public — Accessible wherever the program has access to an object of
the class
• private — Accessible only to member functions of the class
• Protected — Similar to private and discussed later
• Constructor
– Special member function that initialises the data members of a
class object
– Cannot return values
– Have the same name as the class

Objects
• Class definition and declaration
– Once a class has been defined, it can be used as
a type in object, array and pointer declarations
– Example:
Time sunset, // object of type Time
// array of Time objects
// pointer to a Time object
// reference to a Time object
arrayOfTimes[ 5 ],
ime,
= sunset;
*pointerToT
&dinnerTime
Note: The class name
becomes the new type
specifier.

// C++ program to demonstrate accessing of data members
class abc {
//Access specifier
public:
// Data Members
string abcName;
// Member Functions()
void printname() { cout << "AbcName is:" << geekname; }
};
int main()
{
// Declare an object of class geeks
abc obj1;
// accessing data member
obj1.abcName = "Abhi";
// accessing member function
obj1.printname();
return 0;
}

class abc
{
public:
string abcName;
int id;
// printname is not defined inside class definition
void printname();
// printid is defined inside class definition
void printid()
{
cout <<"abc id is: "<<id;
}
};
// Definition of printname using scope resolution operator ::
void Geeks::printname()
{
cout <<"abcName is: "<<abcName;
}
int main() {
Geeks obj1;
obj1.abcName = "xyz";
obj1.id=15;
// call printname()
obj1.printname();
cout << endl;
// call printid()
obj1.printid();
return 0;
}

Implementing with a Class
• Binary scope resolution operator (::)
– Combines the class name with the member function
name
– Different classes can have member functions with the
same name
• Format for defining member functions
ReturnType ClassName::MemberFunctionName( ){
…
}

• If a member function is defined inside the class
– Scope resolution operator and class name are not
needed
– Defining a function outside a class does not change
it being public or private
• Classes encourage software reuse
– Inheritance allows new classes to be derived from
old ones
Implementing with a Class

Class Scope and Accessing Class
Members
• Class scope
– Data members and member functions
• Inside a scope
– Members accessible by all member functions
• Referenced by name
• Outside a scope
– Members are referenced through handles
• An object name, a reference to an object or a pointer to an object

Class Scope and Accessing Class
Members
• Function scope
– Variables only known to function they are defined in
– Variables are destroyed after function completion
• Accessing class members
– Same as structs
– Dot (.) for objects and arrow (->) for pointers
– Example:
• t.hour is the hour element of t
• TimePtr->hour is the hour element

Controlling Access to Members
• public
– Presents clients with a view of the services the class
provides (interface)
– Data and member functions are accessible
• private
– Default access mode
– Data only accessible to member functions and friends
– private members only accessible through the
public class interface using public member
functions

// To demonstrate public
#include<iostream>
using namespace std;
// class definition
class Circle
{
public:
double radius;
double compute_area()
{
return 3.14*radius*radius;
}
};
// main function
int main()
{
Circle obj;
// accessing public datamember outside class
obj.radius = 5.5;
cout << "Radius is: " << obj.radius << "n";
cout << "Area is: " << obj.compute_area();
return 0;
}

// To demonstrate private
#include<iostream>
class Circle
{
// private data member
private:
double radius;
// public member function
public:
double compute_area()
{ // member function can access private
// data member radius
return 3.14*radius*radius;
}
};
// main function
void main()
{
// creating object of the class
Circle obj;
// trying to access private data member
// directly outside the class
obj.radius = 1.5;
cout << "Area is:" << obj.compute_area();
}

// C++ program to demonstrate protected
class Parent
{
// protected data members
protected:
int id_protected;
};
// sub class or derived class from public base class
class Child : public Parent
{
public:
void setId(int id)
{
// Child class is able to access the inherited
// protected data members of base class
id_protected = id;
}
void displayId()
{
cout << "id_protected is: " << id_protected << endl;
}
};
void main() {
Child obj1;
obj1.setId(81);
obj1.displayId();
}

Access Functions and Utility Functions
• Utility functions
– private functions that support the operation of public
functions
– Not intended to be used directly by clients
• Access functions
– public functions that read/display data or check
conditions
– Allow public functions to check private data
• Following example
– Program to take in monthly sales and output the total
– Implementation not shown, only access functions

Class definition
class class_name {
public:
constructor and destructor
member functions
private:
data members
};

InitialiSing Class Objects: Constructors
• Constructors
– InitialiSe class members
– Same name as the class
– No return type
– Member variables can be initialised by the constructor or
set afterwards
• Passing arguments to a constructor
– When an object of a class is declared, initialisers can be
provided
– Format of declaration with initialisers:
Class-type ObjectName( value1, value2,…);
– Default arguments may also be specified in the
constructor prototype

// defining the constructor within the class
#include <iostream>
class student {
int rno;
char name[50];
double fee;
public:
// constructor
student()
{
cout << "Enter the RollNo:";
cin >> rno;
cout << "Enter the Name:";
cin >> name;
cout << "Enter the Fee:";
cin >> fee;
}
void display()
{
cout << endl << rno << "t" << name << "t" << fee;
}
};
int main()
{
student s; // constructor gets called automatically when
// we create the object of the class
s.display();
return 0;
}

// defining the constructor outside the class
#include <iostream>
class student {
int rno;
char name[50];
double fee;
public:
// constructor declaration only
student();
void display();
};
// outside definition of constructor
student::student()
{
cout << "Enter the RollNo:";
cin >> rno;
cout << "Enter the Name:";
cin >> name;
cout << "Enter the Fee:";
cin >> fee;
}
void student::display()
{
cout << endl << rno << "t" << name << "t" << fee;
}
void main()
{
student s;
s.display();
}

Software Reusability
• Software resusability
– Implementation of useful classes
– Class libraries exist to promote reusability
• Allows for construction of programs from existing, well-
defined, carefully tested, well-documented, portable, widely
available components
– Speeds development of powerful, high-quality software

C++ppt. Classs and object, class and object

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