Object oriented programming 13 input stream and devices in cpp

Object Oriented Programming: 13
Input Stream /Extraction Operator
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2
I/O Streams and Standard I/O Devices
• I/O: sequence of bytes (stream of bytes) from
source to destination
– Bytes are usually characters, unless program
requires other types of information
• Stream: sequence of characters from source
to destination
• Input stream: sequence of characters from an
input device to the computer
• Output stream: sequence of characters from
the computer to an output device

3
(continued)
• Use iostream header file to extract
(receive) data from keyboard and send output
to the screen
– Contains definitions of two data types:
• istream - input stream
• ostream - output stream
– Has two variables:
• cin - stands for common input
• cout - stands for common output

4
(continued)
• To use cin and cout, the preprocessor
directive#include <iostream> must be
used
• Variable declaration is similar to:
– istream cin;
– ostream cout;
• Input stream variables: type istream
• Output stream variables: type ostream

5
cin and the Extraction Operator >>
• The syntax of an input statement using cin
and the extraction operator >> is:
• The extraction operator >> is binary
– Left-side operand is an input stream variable
• Example: cin
– Right-side operand is a variable

6
(continued)
• No difference between a single cin with
multiple variables and multiple cin
statements with one variable
• When scanning, >> skips all whitespace
– Blanks and certain nonprintable characters
• >> distinguishes between character 2 and
number 2 by the right-side operand of >>
– If type char or int (or double), the 2 is
treated as a character or as a number 2

7
(continued)
• Entering a char value into an int or
double variable causes serious errors, called
input failure

8
(continued)
• When reading data into a char variable
– >> skips leading whitespace, finds and stores only
the next character
– Reading stops after a single character
• To read data into an int or double variable
– >> skips leading whitespace, reads + or - sign (if
any), reads the digits (including decimal)
– Reading stops on whitespace non-digit character

9
(continued)

Object oriented programming 13 input stream and devices in cpp

11
Using Predefined Functions in a
Program
• Function (subprogram): set of instructions
– When activated, it accomplishes a task
• main executes when a program is run
• Other functions execute only when called
• C++ includes a wealth of functions
– Predefined functions are organized as a collection
of libraries called header files

12
Program (continued)
• Header file may contain several functions
• To use a predefined function, you need the
name of the appropriate header file
– You also need to know:
• Function name
• Number of parameters required
• Type of each parameter
• What the function is going to do

13
Program (continued)
• To use pow (power), include cmath
– Two numeric parameters
– Syntax: pow(x,y) = xy
• x and y are the arguments or parameters
– In pow(2,3), the parameters are 2 and 3

15
Program (continued)
Sample Run:
Line 1: 2 to the power of 6 = 64
Line 4: 12.5 to the power of 3 = 1953.13
Line 5: Square root of 24 = 4.89898
Line 7: u = 181.019
Line 9: Length of str = 20

16
cin and the get Function
• The get function
– Inputs next character (including whitespace)
– Stores in memory location indicated by its
argument
• The syntax of cin and the get function:
varChar
– Is a char variable
– Is the argument (parameter) of the function

17
cin and the ignore Function
• ignore: discards a portion of the input
• The syntax to use the function ignore is:
intExp is an integer expression
chExp is a char expression
• If intExp is a value m, the statement says to
ignore the next m characters or all characters until
the character specified by chExp

18
putback and peek Functions
• putback function
– Places previous character extracted by the get
function from an input stream back to that stream
• peek function
– Returns next character from the input stream
– Does not remove the character from that stream

19
putback and peek Functions
(continued)
• The syntax for putback:
– istreamVar: an input stream variable (cin)
– ch is a char variable
• The syntax for peek:
– istreamVar: an input stream variable (cin)
– ch is a char variable

20
The Dot Notation Between I/O
Stream Variables and I/O Functions
• In the statement
cin.get(ch);
cin and get are two separate identifiers
separated by a dot
• Dot separates the input stream variable name
from the member, or function, name
• In C++, dot is the member access operator

21
Input Failure
• Things can go wrong during execution
• If input data does not match corresponding
variables, program may run into problems
• Trying to read a letter into an int or double
variable will result in an input failure
• If an error occurs when reading data
– Input stream enters the fail state

22
The clear Function
• Once in a fail state, all further I/O statements
using that stream are ignored
• The program continues to execute with
whatever values are stored in variables
– This causes incorrect results
• The clear function restores input stream to
a working state

Assignment
• Explain in detail the functioning of Input
Stream Operator
• What do you understand by Input Failure and
what is the role of clear function

Object oriented programming 13 input stream and devices in cpp

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