DATA INPUT AND OUTPUT

SINGLE CHARACTER INPUT - THE getchar( ) FUNCTION
Single characters can be entered in to the computer using the C library function getchar( ). The getchar function is a part of the standard C Language i/o Library. It returns a single character from a standard input device. The function does not require any arguments, though a pair of empty parentheses must follow the word getchar.
In general terms a reference to the getchar function is written as:-
character variable = getchar( );
Here character variable refers to some previously declared character variable


SINGLE CHARACTER OUTPUT-THE putchar( ) FUNTION
The putchar( ) function, like getchar( ), is a part of the standard C language i/o library. It transmits a single character to a standard output device. The character being transmitted will normally be represented as a character- type variable. It must be expressed as an argument to the function enclosed in parentheses following the word putchar.
In general a reference to the putchar function is written as . putchar( char var )

e.q A C-Program contains the following statement :
char C;
_
_
_
_
putchar(C);
The first statement declares that C is a character type variable. The second statement causes the current value of C to be transmitted to the standard output device.

ENTERING INPUT DATA THE scanf( ) FUNTION
Input data can be entered into the computer from a standard input device by means of the C
library function scanf().
In general terms, the scanf function is written as scanf(Control string, arg1,arg2,.....,argn)
Here control string refers to a string containing certain required formatting information, and arg1, arg2,...arg n are arguments that represent the individual input data items. The argu- ments represent pointers that indicate the addresses of the data item within the computers memory.

The control string comprises individual groups of characters with one character group for each input data item. Each character group must begin with a a percent sign( % ). In its simplest form a single character group will consist of the percent sign, followed by a conver- sion character which indicates the type of the corresponding data item.

COMMONLY USED CONVERSION CHARACTERS FOR DATA INPUT

Conversion character	Meaning
c	data item is a single character
d	data item is a decimal integer
f	data item is a floating point value
h	data item is a short integer
I	data item is a decimal, hexadecimal or octal integer
o	data item is an octal integer
s	data item is a string followed by white space character
u	data item is an unsigned decimal integer
x	data item is a hexadecimal integer

e.q of scanf function
# include "stdio.h"
main( )
{
char item [20];
int partno;
float cost;
. . .
scanf(“%s% d % f”, item, &partno, & cost);
. . .
}
The first character group % s indicates that the first argument (item) represents a string the
second character group, %d indicates that the second argument ( & partno) represents a decimal integer value. The third character group % f, indicates that the third argument (& cost) represents a floating point value.
e.q. consider the skeleton of the following program
# include "stdio.h"
main( )
{
char item [20];
int partno;
float cost;
. . .
scant(“%s%d%f”, item &partno, &scost);
}
The following data items could be entered from the standard input device when the program is executed.
fastener 12345 0.05
or
fastener
12345
0.0 5
Now let us again consider the skeleton structure of a C program
# include "stdio.h"
main ( )
{
int a,b,c;
. . .
scanf (“%3d %3d %3d”, & a, & b, & c);
. . .
}
Suppose the input data items are entered as
1 2 3
Then the following assignment is will result a = 1, b = 2, c = 3
It data is entered as
123 456 789
The following assignments would be
a = 123, b = 456, c = 789
Now suppose that the data had been entered as
123456789
The assignments would be
a = 123, b = 456, c = 789
Again consider the following example
# include "stdio.h"
main ( )
{ int i ; float x; char c ;
. . .
scanf (“%3d %5f %c”, & i, & x, & c);
. . .
}
If the data item are entered as
10256.875 T
These when the program will be executed
10 will be assigned to i
256.8 will be assigned to x
and the character 7 will be assigned to c. the remaining two input characters(5 and T) will be ignored.

WRITING OUTPUT DATA - THE printf( ) FUNCTION
Output data can be written from the computer on to a standard output device using the library function printf the general form of printf function is
printf(control string, arg 1, arg 2, . . ., argn)
where control string refers to a string that contains formatting information.
arg1, arg 2, . . ., argn are arguments that represent the individual output data items.
e.g:- Following is a simple program that makes use of the printf function.
# include"stdio.h"
# include conio.h"
main ( ) /* Print several floating-point numbers */
{
float i = 2.0, j = 3.0 ;
printf (“%f %f %f %f”, i, j, i+j, sqrt (i + j ));
}
Executing the program produces the following output
2.000000 3.000000 5.000000 2.236068


The gets( ) and puts( ) FUCTIONS
The gets and puts are the functions which facilitate the transfer of strings between the com- puter and the standard input/output devices.
Each of these functions accepts a single argument.
The argument must be a data item that represents a string (e.g, a character array). The string may include white space characters. In the case of gets, the string will be entered from the keyboard and will terminate with a newline character (“i’e” the string will end when the user presses the RETURN key).
# include "stdio.h"
main ( )
{
char line [80]; gets(line); puts(line);
}
Now suppose following string is entered from the standard input device
I am happy
Now the output of the program will be
I am happy