How to perform I/O operation in c++

 What is input ?

• Information given to the program, is called input
• In input data is flow inside the program
• It required a source(for reading )

stadin - - > standard input used as scanf function

stdout --->  standard input used as printf function taken by monitor(gives destination)

What is output :

• Information given by the program is called output
• In output data is flow outside the program
• In c++ I/O operations are alone using streams
• A stream is class is provide set of functions to perform input and output operations
• A stream represents input source (reading) and output destination (writing)
• C++ provides 2 stream classes

1. ostream
2. istream

• .IIstream The istream consists of input functions to read a streams of characters from the keyboard.

• Ostream The ostream consists of output functions to write a character onto the screen.

stdout is a file pointer which is pointing to console

 I/O operation in C++ Example

Cout ->

• It is a predefined object of class Ostream
• Cout represent console output
• Cout represent standard output devide(Monitor)
• For cout object destination is standard output device
• Ostream cout(“ con ”);
• This predefined object is a variable in IOstream.h file
• This object uses << (insertion) operator to perform formatted output operation
• This object uses all the member function of stream class to perform output operation
• << ( insertion operator) is overloaded operation on member function

ex : printf(“%d”,IO)//                               This operation performs O/P operation without using formatting specifier.

printf(“%f”,1.5)

• This operation insert one values
• Insertion means writing / printing Cout << ’10,20 ; // it will print 10

Syntax :

cout<< variable/constant/expression;

In order to print multiple values cout uses multiple insertion operators.

Cout<value 1<value2<value 3…….

• Using multiple insertion operator with cout is called cascading , it is a method of organizing
• evaluation of insertion operators are are done from right to left and insertion is done from left to right

Example :

# include<iostream.h>

void main()

{

cout<< “welcome to c++”;

}

Eg :-

#include <iostream.h>

void main()

{

cout<<10;                 // cout <<10<<end l;

cout<< 1.5;                // cout<<1.5<<end l;

cout << ‘A’;                  // cout<<’A’<<end l;

cout<<1/5;                  // cout<<1.5<<end l;

cout<<’A’;                    // cout << ‘A’ << end l;

cout<< “c++”               // cout << “c++” <<endl;

}

endl : It is a manipulator used for inserting new line

1. Q) What is the difference between \n and endl ?

In is a back slash is escape sequences

eg:

# include <iostream.h>

void main()

{

cout<<10<<1.5<<’A’<<”c++”;     // cascading

}

Cin : It is an object of istream class.

• istream class provide set of functions to performs input operations
• Cin uses >> (extraction) operation to read any type of value
• It does not required any formatting specifiers

Formatting is an implicit functionality of extract of operation

• It is an overloaded operation // reading (source) writing Cdestination which extend functionality of >> (shift operator)

syntax :

Cin >> variable –name;

• One extraction operator read only one value cin>>var1>>var2>>var3----
• Using multiple extraction is called as cascading

Variable (local) :

The variable declared inside function is called local variable.

• Memory for this variable is allocated on execution of function and after completion of function
• The scope of this variable within function
• Local variable are called auto variable.
• Auto is storage class and variable is never declared without class
• Storage class define scope life time and storage of variable.

Eg :

#include<iostream.h>

void main()

{

int x;

int Y;

int Z;

Cout << X << endl;

cout<<Z<<endl;

}

o/p : The output of above program is garbage value, Because local variables are not given any default values.

• C++ allows to declare local variable anywhere within function

eg :

# include <iostream.h>

void main()

{

int n1;

cout<< “\n input n1 value”;

cin >> n1;

int n2;

cout<< “\n input n2 value”;

cin>> n2;

int n3;

n3=n1+n2;

cout<< “\n sum is ” << n3

}

C++ allows to declare block level variables