Classes and objects

Class
• A class is an organization of data and functions
which operate on them.
• Data structures are called data members and the
functions are called member functions.
• The combination of data members and member
functions constitute a data object or simply an
object.

Object
• Instantiation of a class.
• In terms of variables, class would be the type and
an object would be a variable.

General Structure of a class
• Class name or name of class
• Data Members
• Member functions
• Access Specifiers
• Declaring objects

Classes in C++
• A class definition begins with the keyword class.
• The body of the class is contained within a set of
braces, { } ; (notice the semi-colon).
class class_name
{
….
….
….
};
Class body (data member +
methods)
Any valid
identifier

class classname
{
private:
variable declarations;
function declarations;
public:
protected:
} obj1, obj2,…..objN;

Class name
• Name given to a particular class.
• Serves as a name specifier for the class using which
we can create objects.
• The class is specified by keyword “class”

Data Members
• Data type properties that describe the
characteristics of a class.
• We can declare any number of data members of
any type in a class.
• We can say that variables in C and data members in
C++.
• E.g. int rn;

Member functions
• Various operations that can be performed to data
members of that class.
• We can declare any number of member functions
of any type in a class.
• E.g. void read();

Access Specifiers
Used to specify access rights for the data members
and member functions of the class.
Depending upon the access level of a class member,
access to it is allowed or denied.
Within the body, the keywords private: and public:
specify the access level of the members of the class.
the default is private.
Usually, the data members of a class are declared in
the private: section of the class and the member
functions are in public: section.

Classes in C++
class class_name
{
private:
…
…
…
public:
…
…
…
};
Public members or methods
private members or
methods

Private:
only members of that class have accessibility
 can be accessed only through member functions of
that class.
Private members and methods are for internal
use only.

Public:
• Accessible from outside the class
• can be accessed through member function of any
class in the same program.

Protected:
• Stage between private and public access.
• They cannot be accessed from outside the class, but
can be accessed from the derived
class.(inheritance)

Class Example
• This class example shows how we can encapsulate
(gather) a circle information into one package (unit
or class)
class Circle
{
private:
double radius;
public:
void setRadius(double r);
double getDiameter();
double getArea();
double getCircumference();
};
No need for others classes to
access and retrieve its value
directly. The
class methods are responsible for
that only.
They are accessible from outside
the class, and they can access the
member (radius)

C++ supports three access specifiers:
public
private
protected
The public access specifier allows a class to subject its
member variables and member functions to other functions
and objects
The private access specifier allows a class to hide its
member variables and member functions from other class
objects and functions
The protected access specifier allows a class to hide its
member variables and member functions from other class
objects and functions just like private access specifier - is
used while implementing inheritance

Declaring objects:
A class declaration only uses to build the structure
of an object.
Declaration of an object is same as declaration of
class.
Defining objects of class data type is known as class
instantiation(instances of class)
When we create objects during that moment ,
memory is allocated to them.
• Ex- Circle c;

class Customer
{
void accept()
{
cout << “Accepting Customer Details” << endl;
}
void display()
{
cout << “Displaying Customer Details” << endl;
}
};
Void main()
{
Customer C1;
C1.accept();
C1.display();
getch();
}

#include<iostream.h>
#include<conio.h>
class student
{
private:
int rollno;
char name[10];
public:
void get();
void display();
};
void student::get()
{
cout<<"Enter Roll Number=";
cin>>rollno;
cout<<"Enter Name=";
cin>>name;
}
void student::display()
{
cout<<"Roll Number="<<rollno<<endl;
cout<<"Name="<<name<<endl;
}
int main()
{
student s1;
clrscr();
s1.get();
s1.display();
getch();
return 0;
}

Classes and objects

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Classes and objects