CPU INPUT OUTPUT

INPUT OUTPUT
FUNCTIONS IN C
PROGRAMMING
COMPUTER
PROGRAMMING AND
UTILIZATION

Introduction
 Reading input data, processing it and
displaying the results are the three tasks of
any program.
 There are two ways to accept the data.
 In one method, a data value is assigned to the
variable with an assignment statement.
 Another way of accepting the data is with
functions.

Formatted function
• With the formatted functions, the input or
output is formatted as per our
requirement.
• All the I/O function are defined as
stdio.hstdio.h header file.
• Header file should be included in the
program at the beginning.

Input and Output Functions
Formatted Functions Unformatted Functions
printf()
scanf()
getch() putch()
getche() putchar()
getchar() puts()
gets()

Formatted Functions
It read and write all
types of data values.
Require format string
to produce
formatted result
Returns value after
execution
Unformatted Functions
Works only with
character data type
Do not require format
conversion for
formatting data type

printf( ) function
This function displays output with specified
format
It requires format conversion symbol or format
string and variables names to the print the data
The list of variables are specified in the printf()
statement
The values of the variables are printed as the
sequence mentioned in printf()
The format string symbol and variable name
should be the same in number and type

printf( ) function
Syntax
printf(“control string”, varialbe1,
variable2,..., variableN);
 The control string specifies the field format
such as %d, %s, %g, %f and variables as
taken by the programmer

void main()
{
int NumInt = 2;
float NumFloat=2.2;
char LetterCh = ‘C’;
printf(“%d %f %c”, NumInt, NumFloat, LetterCh);
}
Output :
2 2.2000 C

void main()
{
int NumInt = 65;
clrscr();
printf(“%c %d”, NumInt, NumInt);
}
Output :
A 65

void main()
{
int NumInt = 7;
clrscr();
printf(“%f”, NumInt);
return 0;
}
Output :
Error Message : “Floating points formats not linked”

 All the format specification starts with
% and a format specification letter
after this symbol.
 It indicates the type of data and its
format.
 If the format string does not match
with the corresponding variable, the
result will not be correct.
 Along with format specification use
 Flags
 Width
 Precision

 Flag
 It is used for output justification,
numeric signs, decimal points, trailing
zeros.
 The flag (-) justifies the result. If it is
not given the default result is right
justification.
 Width
 It sets the minimum field width for an
output value.
 Width can be specified through a
decimal point or using an asterisk ‘*’.

void main()
{
clrscr();
printf(“n%.2s”,”abcdef”);
}
OUTPUT
ab
abc
abcd

void main()
{
int x=55, y=33;
clrscr();
printf(“n %3d”, x – y);
printf(“n %6d”, x – y);
}
OUTPUT
22
22

void main()
{
int x=55, y=33;
clrscr();
printf(“n %*d”, 15, x – y);
printf(“n %*d”, 5,x – y);
}
OUTPUT
22
22

void main()
{
float g=123.456789;
clrscr();
printf(“n %.1f”, g);
}
OUTPUT
123.5
123.46
123.457
123.4568

scanf() function
 scanf() function reads all the types of data
values.
 It is used for runtime assignment of
variables.
 The scanf() statement also requires
conversion symbol to identify the data to be
read during the execution of the program.
 The scanf() stops functioning when some
input entered does not match format string.

scanf() function
Syntax :
scanf(“%d %f %c”, &a, &b, &c);
 Scanf statement requires ‘&’ operator called
address operator
 The address operator prints the memory
location of the variable
 scanf() statement the role of ‘&’ operator is to
indicate the memory location of the variable,
so that the value read would be placed at that
location.

scanf() function
 The scanf() function statement also
return values. The return value is
exactly equal to the number of values
correctly read.
 If the read value is convertible to the
given format, conversion is made.

void main()
{
int a;
clrscr();
printf(“Enter value of ‘A’ : “);
scanf(“%c”, &a);
printf(“A : %c”,a);
}
OUTPUT
Enter value of ‘A’ : 8
A : 8

void main()
{
char a;
clrscr();
printf(“Enter value of ‘A’ : “);
scanf(“%d”, &a);
printf(“A : %d”,a);
}
OUTPUT
A : 255
A : 256

Data Type Format string
Integer Short Integer %d or %i
Short unsigned %u
Long signed %ld
Long unsigned %lu
Unsigned hexadecimal %u
Unsigned octal %o
Real Floating %f or %g
Double Floating %lf
Character Signed Character %c
Unsigned Character %c
String %s
Octal number %o
Displays Hexa
decimal number in
lowercase
%hx
Displays Hexa
decimal number in
lowercase
%p

void main()
{
int a = 1, b = a + 1, c = b + 1, d = c + 1;
clrscr();
printf(“t A = %dnB = %d ’C = %d’”,a,b,c);
printf(“nb***D = %d**”,d);
printf(“n*************”);
printf(“rA = %d B = %d”, a, b);
}
OUTPUT
A = 1
B = 2 ‘C = 3’
***D=4**
A = 1 B = 2******

Unformatted Functions
C has three types of I/O functions
 Character I/O
 String I/O
 File I/O
 Character I/O

getchar ( )
 This function reads a character type
data from standard input.
 It reads one character at a time till
the user presses the enter key.
 Syntax
VariableName = getchar();
 Example
char c;
c = getchar();

putchar( )
 This function prints one character on the
screen at a time, read by the standard
input.
 Syntax
 puncher(variableName)
 Example
char c = ‘C’;
putchar(c);

getch() and getche()
 These functions read any
alphanumeric character from the
standard input device.
 The character entered is not displayed
by the getch() function.
 The character entered is displayed by
the getche() function.
 Exampe
 ch = getch();
 ch = getche();

gets()
 This function is used for accepting any string through stdin keyword until
enter key is pressed.
 The header file stdio.h is needed for implementing the above function.
 Syntax
char str[length of string in number];
gets(str);
void main()
{
char ch[30];
clrscr();
printf(“Enter the string : “);
gets();
printf(“n Entered string : %s”, ch);
}

puts()
 This function prints the string or character array.
 It is opposite to gets()
char str[length of string in number];
gets(str);
puts(str);

CPU INPUT OUTPUT

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