InputOutput

1
Input/Output

• Reading Chapter 3

2
C streams

• No I/O is built into C
• C allows generalized Input/Output through a
  mechanism called a stream

3
C streams

• The C I/O library defines
• Input stream (istream) sequence of characters
  coming into a program from an input device
• Output stream (ostream) sequence of characters
  going from a program to an output device

4
C streams

• To use stream I/O, program should have
• include ltiostreamgt
• using namespace std
• The ltiostreamgt defines
• An input stream (istream) object named cin
• Pronounced see-in
• Associated with the standard input device
  (keyboard)
• An output stream (ostream) object named cout
• Pronounced see-out
• Associated with the standard output device
  (screen)

5
Extraction operator

• The stream extraction operator gtgt extracts input
  from the input stream and stores it in a
  variable.
• Example
• cin gtgt age
• The gtgt is a binary operator
• Also known as get from
• The left operand is an input stream object, such
  as cin
• The right operand is a variable of simple type
• Has left-to-right associativity

6
Extraction operator (Cont..)

• The gtgt operator can be used more than one time in
  the same statement
• cin gtgt age gtgt weight
• Input values are separated by whitespaces
  (blanks, tabs, newlines)
• The gtgt operator skips over (actually reads but
  does not store anywhere) leading white space
  characters as it reads your data from the input
  stream

7
Example

• include ltiostreamgt
• using namespace std
• int main()
• int someInt
• float someFloat
• cout ltlt "Enter an integer followed by a float
  "
• cin gtgt someInt gtgt someFloat
• cout ltlt "Integer " ltlt someInt ltlt endl
• ltlt "Float " ltlt someFloat ltlt endl
• return 0

8
Output
Enter an integer followed by a float 34
5.65 Integer 34 Float 5.65
9
Insertion Operator

• The stream insertion operator ltlt inserts data
  into the output stream.
• Example
• cout ltlt 34
• The ltlt is a binary operator
• Also known as put to
• The left operand is an output stream object, such
  as cout
• The right operand is an expression of simple type
  or a string constant
• Has left-to-right associativity

10
Insertion operator (Cont..)

• The ltlt operator can be used more than one time in
  the same statement
• cout ltlt "The answer is" ltlt 34
• Output is stored in a buffer until
• the buffer becomes full
• the program terminates
• an endl is inserted in the output stream

11
The endl manipulator

• Used to terminate the current output line
• Used to create blank lines in output
• Example
• cout ltlt "The answer is" ltlt 34 ltlt endl

12
Special ASCII characters

• Special characters have a backslash (\) followed
  by a printable character
• Can be used with ltlt operator

\0 Null \a Audible alarm \b Backspace \n New line
\r Carriage Return \t Horizontal
tab \" Quote \\ Backslash
13
Class Assignment

• You have to write a C program to calculate the
  salary of a worker. The salary is calculated by
  multiplying the number of hours he has worked
  with the hourly wage. Ask the user to enter
  values for the number of hours and the hourly
  wage. Finally display the salary with 2 digits
  after the decimal points.