Basic Input/Output
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Introduction
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Input refers to accepting data while output refers
to presenting data. Every program performs three main functions accepting
data from user, processing it and producing the output.
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In C language there are several input and output functions.
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These functions are collectively
found in IO.h and such IO function together
form a library namestdio.h .
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User will require all such library
function.
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These library functions are
classified into three broad categories:
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1. Console I/O functions
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2. Disc I/O functions
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3. Port I/O functions
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Console I/O function
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Console I/O refers to the operation
that occur at the keyboard and the screen of your computer.
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Console I/O function can also be
classified in two parts:
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1. Formatted console I/O:
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Formatted I/O function accepts or present
in a particular format. The example of formatted console I/O function
is printf( ) and scanf( ).
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printf
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It is highly desirable that the output are
presented in such a way that they are understandable and are in a form easy
to use.
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The printf() statement
provides certain features through which the screen output is
effectively controlled.
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The general form of printf() function
is:
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printf("Control String
",arg1,arg2....);
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Control string may contain:
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1. character that are simply printed
as they are.
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2. Conversion specification that
begin with a sign.
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3. Escape sequence that begin with \
sign.
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Given below is a list of conversion
charcter that can be used with printf() function:
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scanf
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scanf allows formatted reading of data from the
keyboard. Like printf it has a control string, followed by
the list of items to be read.
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However scanf wants
to know the address of the items to be read, since it is a function which
will change that value. Therefore the names of variables are preceeded by the
& sign.
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Character strings are an exception to
this. Since a string is already a character pointer, we give the names of
string variables unmodified by a leading &.
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Control string entries which match
values to be read are preceeded by the percentage sign in a similar way to
their printf equivalents.
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2. Unformatted console I/O:
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This function cannot control the
format of reading and writing the data. some of the example of this function
are getch( ),getche( ),getchar( ),gets( ),putchar( ),putch( )and puts(
).
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getchar
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getchar returns the next character of
keyboard input as an int.
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If there is an error then EOF (end
of file) is returned instead. It is therefore useful to compare this value
against EOF before using it.
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If the return value is stored in a char, it
will never be equal to EOF, so error conditions will not be
handled correctly.
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putchar
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putchar puts its character argument on the
standard output (usually the screen).
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The following example program
converts any typed input into capital letters.
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To do this it applies the function
toupper from the character conversion library ctype.h to each character in
turn.
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gets
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gets reads a whole line of input into
a string until a newline or EOF is encountered. It is
critical to ensure that the string is large enough to hold any expected input
lines. When all input is finished,NULL as
defined in stdio.h is returned
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puts
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puts writes a string to the output,
and follows it with a newline character.
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Note: putchar, printf and puts can
be freely used together. So can getchar, scanf and gets.
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Disc & Port I/O function
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Function which performs secondary
storage devices like floppy disk or hard disk is called disk I/O
functions.
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Port I/O functions
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This type of functions performs I/O operation
among various codes like printer port, mouse port.
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