Concepts and Basics of C++
Programming
Contents
 Object
 Class
 Inside the class definition of member function
 Outside the class definition of member function.
 Cout /Cin
 Access specifiers.
 Accessing the class members through object.
 Inline and non Inline function.
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Object-Orientation
 A thinking methodology
 Everything is an object.
 Any system is composed of objects (a system is also an
object).
 The evolution and development of a system is caused by the
interactions of the objects inside/outside a system.
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Everything is an object
 A student, a professor
 A desk, a chair, a classroom, a building
 A university, a city, a country
 The world, the universe
 A subject such as CS, IS, Math, History, …
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The development of a system is caused by
interactions
 University is defined by the interactions among:
 students
 professors
 staff
 Board governance
Inside
University
 State governance
 … ...
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Outside
University
Reading and Writing Data
Reading and Writing Data
 Two operators are introduced in c++ i.e. cout and cin.
 Cout is a predefined object and represents the standard output
stream and this output stream represents the screen. Cout, equires
iostream file
E.g. cout<<“ I love india”;
cout will display this string as such on screen.
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 << is called insertion or put to operator.
 It is also called bit-wise left -shift operator
 if string is variable then cout can be used to display the
contents of string.
E.g. cout<< string;
 cin is used to read the data.
 cin>>a;
 >> is called extraction operator.
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The cout Object
 Displays output on the computer screen
 You use the stream insertion operator << to send
output to cout:
cout << "Programming is fun!";
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The cout Object
 Can be used to send more than one item to cout:
cout << "Hello " << "there!";
Or:
cout << "Hello ";
cout << "there!";
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The cout Object
 This produces one line of output:
cout << "Programming is ";
cout << "fun!";
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The cin Object
 Standard input object
 Like cout, requires iostream file
 Used to read input from keyboard
 Information retrieved from cin with >>
 Input is stored in one or more variables
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The cin Object
 cin converts data to the type that matches the variable:
int height;
cout << "How tall is the room? ";
cin >> height;
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The cin Object
 Can be used to input more than one value:
cin >> height >> width;
 Multiple values from keyboard must be separated
by spaces
 Order is important: first value entered goes to
first variable, etc.
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Reading Strings with cin
 Can be used to read in a string
 Must first declare an array to hold characters in
string:
char myName[21];
 myName is name of array, 21 is the number of
characters that can be stored (the size of the array),
including the NULL character at the end
 Can be used with cin to assign a value:
cin >> myName;
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Class
 A class is a user define data type which holds both data
and function.
 The data included in the class i.e the internal data is
called data member and the functions included is
called the member function.
 These member functions can manipulate the internal
data of the class
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Object
 Is an instant of a class.
 In terms of variables, class would be the type and an
object would be a variable.
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Creating 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
{
….
….
….
};
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Any valid
identifier
Class body (data member +
methods)
class classname
{
private:
variable declarations;
function declarations;
public:
variable declarations;
function declarations;
protected:
variable declarations;
function declarations;
} obj1, obj2,…..objN;
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Class name
 Name given to a particular class (any user define
name). It can also be called as tag name of the class
that act as the type specifier for class using which we
can create objects.
 The class is specified by keyword “class”
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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.
E.g. int x;
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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();
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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.
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class class_name
{
private:
…
…
…
public:
…
…
…
};
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private members or methods
Public members or methods
Private:
only members of that class have accessibility
 can be accessed only through member functions of that
class i.e by the functions declared inside the class only.
 Private members and methods are for internal
use only.
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Public:
 Accessible from both inside and outside the class also i.e
by the functions declared in the main() program also.
Protected:
 Stage between private and public access.
 They can be accessed by the member function or friend
functions of the class. They are similar to private members
in the sense that they cannot be accessed by the nonmember functions of the class.
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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();
};
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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)
Methods definition
• The member function of the class can be defined in two
different ways:
1) Inside the class definition:- The member functions are
simple defined inside the class only i.e the body of the
function resides inside the range of class only.
2) Outside the class definition: by using scope resolution
operator, which specifies that the scope of the function is
restricted to the class class_name.
Syntax:- class_name:: function_name
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Inside the class definition
Eg: class abc
{
private:
int rollno;
char name[20];
public:
void getdata()
{
cout<<“name=“;
cin>>name;
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cout<<“rollno=“;
cin>>rollno;
}
void display()
{
cout<<“name=“<<name;
cout<<“rollno=“<<rollno;
}
};
Outside the class definition
Eg: class abc
{
private:
int rollno;
char name[20];
public:
void getdata();
void display();
};
void abc :: getdata()
{
cout<<“name=“;
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cin>>name;
cout<<“rollno=“;
cin>>rollno;
}
void abc :: display()
{
cout<<“name and rollno=“;
cout<<name<<rollno;
}
INLINE AND NON INLINE MEMBER
FUNCTION
 A function defined inside the class is by default inline
function
 A function defined outside the class using scope
resolution operation is non-inline function. It can be
made inline by using keyword inline before the
function definition.
Eg.
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inline void abc::getdata()
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Declaring objects
 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- class Circle c;
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class book
{
private:
int p; char n[40];
public:
void getdata()
{
cout<<“enter book price”;
cin>>p;
cout<<“enter book name”;
cin>>n; }
void display(); };
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void book ::display()
{
cout<<“book name=“<<n;
cout<<“book price=“<<p;
}
void main()
{
class book obj;
obj.getdata();
obj.display();
}
Accessing class members
 Public members of class can be accessed using dot(.)
operator with the object name.
 Private members of the class are accessed inside the
public member functions of class.
Eg: obj.getdata();
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