I/O operation in C++

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21st September, 2018




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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 Screenshot_3  

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  


it is called manipulator it is called escape sequence
It doesn’t occupy any space It occupy 1 byte
It is available in iostream.h it is available in ‘C’

      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  

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