The document discusses input/output (I/O) streams in C++. It explains that I/O is handled by the iostream library using stream-based classes like istream and ostream. The extraction (>>) and insertion (<<) operators allow input from and output to these streams. Overloading these operators allows user-defined types to be read from and written to streams. This is done by declaring friend operator functions that take a stream and class reference.

3.  In C++ programming language, Input/output
library refers to a family of class templates
and supporting functions in the C++
Standard Library that implement stream-
based input/output capabilities.
 These class templates are available in
#include<iostream>

5.  The iostream class can handle both input and
output, allowing bidirectional I/O.
 There are two iostream operators are
available. They are,
 ISTREAM (>>)
 OSTREAM (<<)

6.  The istream class is the primary class used
when dealing with input streams.
 For input streams, the extraction operator
(>>) is used.
 when the user presses a key on the keyboard,
the key code is placed in an input stream.

7.  The ostream class is the primary class used
for dealing with output streams.
 For output streams, the insertion operator
(<<) is used to put values in the output
stream.
 We insert our values into the stream, and the
data consumer (eg. monitor) uses them.

9.  The ostream operator (i.e) insertion operator
(<<) can be overloaded.
 It is both a bitwise left-shift operator and an
output operator, it is called as Insertion
operator when it is used for output.
 It acts as an output operator only when cout
(output stream object) appears on the left
side.
 The preceding function, called operator <<(),
returns a reference to ostream.

10.  C++ overloads the << operator to work with
the built-in data types, we also may overload
the << operator to work with our own
classes.
 It must have two arguments,
 a reference to ostream (it can be of any
name)
 an reference object to the class

11. Declaration,
friend ostream &operator <<(ostream &out,
const classType &x) ;
Function Definition,
ostream &operator <<(ostream &out, const
calssType &x)
{
return out;
}

12.  Using rational class,
Declaration
friend ostream &operator <<(ostream &out, rational
&d);
Definition
ostream &operator <<(ostream &out, const rational
&d)
{
out<<“nNumerator:<<d.nr<<“n”<<“Denomina
tor: ”<<d.dr;
return out;
}

13.  The istream operator (i.e) extraction operator
(>>) can also be overloaded.
 It is both a bitwise right-shift operator and an
input operator, it is called as Extraction
operator when it is used for input.
 It acts as an input operator only when
cin(input stream object) appears on the left
side.
 The preceding function, called operator>>(),
returns a reference to istream.

14.  It must have two arguments,
 a reference to istream (it can be of any
name)
 an reference object to the class.

15. Declaration,
friend istream& operator >>(istream &in,
classType &x) ;
Function Definition,
istream& operator>>(istream &in ,calssType &x)
{
return in;
}

16.  Using rational class,
Declaration
friend istream& operator >>(istream &in, rational
&d);
Definition
istream& operator >>(istream &in, rational &d)
{
cout<<"nEnter the numerator and
denominator”;
in>>d.nr>>d.dr;
return in;
}

18. using namespace std;
#include<iostream>
class rational
{
int nr,dr;
public:
rational addRational(rational r1)
{
rational temp;
temp.nr=nr+r1.nr;
temp.dr=dr;
return temp;
}

19. friend istream &operator >>(istream &in,rational
&d)
{
cout<<"nEnter the nr and dr: ";
in>>d.nr>>d.dr;
return in;
}
friend ostream &operator <<(ostream &out,const
rational &d )
{
out<<"nNr: "<<d.nr<<"nDr:
"<<d.dr;
return out;
}
};

20. //defined outside the class (optional)
/*istream &operator >>(istream &in,rational &d)
{
cout<<"nEnter the value";
in>>d.nr>>d.dr;
return in;
}
ostream &operator <<(ostream &out,const rational
&d)
{
out<<"nr: "<<d.nr<<"Dr: "<<d.dr;
return out;
}*/

21. int main()
{
rational r1,r2;
cin>>r1;
cin>>r2;
rational r3=r1.addRational(r2);
cout<<r3;
}

23.  We can’t overload the iostream operator
using the member function.
 For overloading binary operator we need two
arguments has to passed.
 But here we can’t able to pass the istream or
ostream reference object (i.e) cin or cout
objects are not passed.
 So we can’t able to overload the cin, cout
using member function.

24.  If we want to overload iostream by member
function we want to add definions into header
files and library files for corresponding
objects.
 Thus, the overloading of iostream operators
can be achieved only through friend function.

25.  http://www.tutorialspoint.com/cplusplus/inp
ut_output_operators_overloading.htm
 http://www.learncpp.com/cpptutorial/31inpu
tandoutputiostreams/