Unit‐II
DATA INPUT AND OUTPUT
Reading processing and writing of data are the three essential functions of a
computer program all input and output operations are carried out through a function such as
scanf and printf these function are known as the standard I/o library
#include <studio.h>
The file name studio.h is an abberivation for standard input – output header file the header
file tells the compiler to search for a file named stdio.h and places its contents at his poits in
the program the content of the header file become part of the source code when it is complied
Reading a charcter :
The simplest input/output operations is reading a charcter from the standard
input (keyword) and weritting is to be the standard output unit (screen) reading a single
charcter can be done by using getchar function
Syntax : variable name = getchar();
Variable name is a valid C that has been described as char data type
When its statement is encounted complier waits until a key is pressed and then assigns a
charcter as a value to getchar function
EX
Char course;
Course =getchar ();
Writng a charctrer :
Putchar() functions is used for writing one charcter at a time to the terminal
Syntax : putchar (variables name);
When variables name is atype char variable containg a charcter
Ex
Ans=’y’;
Putchar( ans );
2 formatted input
It refer to an input data that has been arranged in a particular format
Syntax :
Scanf (“control strings” ,&arg1,&arg2…………..,&argn);
Controls string specifies the field format in which the data is to be entered
Argunments arg1, arg2….argn specify the address of location where the data is stored
Control strings and argunments are seprated by commas
Controls srring may include
*field specification consisting of conversion charcters % a data type charcter (or)type
specified and an optional number , specifying field with
* blanks tabs ot newline
Blanks and new lines are ignored
The field width specified is optional
A) INPUTING INTERGER NUMBER:
The field specification for reading on integer number is
%WD
The percentage sign indication that is a conversion specification follows
W is a integer number that specifies the field width of the number to be read
D is known as data type charcter
EX scanf (“%d”,d”&num );
Data; 100
The value is 100 is assigned to num
Input data items must be seprated by spaces tabs or newline
Puinctuation marks do not count as separator
As input field may be skipped by specifying ‘*’in the place of field with
Ex :
Scanf(“%d%*d%d”,&a,&B):
Will assign the data 123 456 738
A=123
456 is skipped because of*;
B=738
If we enter floating point value instead of an integer the fraction part may be skipped
away and also scanf may skip further input reading
INPUTING REAL NUMBERS
Field width of real numbers need not be specified
Scanf reads real number using simple specification % for both decimal point notation
and expontential notation
Ex
Scanf (%f%f%”,&x&y.&z):
With the input data
475.89 48.2 e-1 678
Will assign the value 475.89 to x .4821` to y , 678 0to z
Input fields specifications may be separators by any arbitrary blank spaces
If the number to be read is of double of then the specification should be % 1f
A number may be skipped using %*f specification
Inputting charcter string
Scanf function can input stringd containing more than one charcter
The field specification for reading a charcter strings
%ws or %wc
%c way be used to read a single charcter when the charcter when the argunments is a
pointer to a char variable
Commonly used scanf format codes
Formatted output
General form of printf statement
Printf ( “control strings”,args1 , args2,…..argn);
Control string consists of three types
*charcters will be printed on the screen as they appear
* format specification
* escape sequences
* control string indicates how may argunments follows and what their types are
Format
%w.p type_ specifier
Where w is an interger number that specifies the total number of columns for output
value
P is an integer number that specifies the number of digits to the right of the decimal
point
Both p and w are optional
Output of integer number :
The syntax for an integer number
%WD
Where w specifies the minimum field with for the output
If a number is greater than the specifies field width it will be printed in full
D specifies that the value to be printed is an integer
Ex
Format output
1. Printf(“%d”,9876); 9876
2. Printf(“%6d”.9876); 9876
3. Printf(“%6d”,8976); 9876
Left justified can be achived by piecing a minus sign directly after the % charcter
It is also possible to pad with zeros the leading blanks by placing a zero before thr
field width specified
Printf(“%06d”.9876); 009876
Long integer may be printed by specified id the place of d where 1 denotes the long
qualifier
OUTPUT OF REAL NUMBER
Output of real number may be displayed in decimal function
%w.pf
W-> indicates the minimum number of positions that are to be used for the display of
the value
P-> the number of digit to be displayed after the decimal point
The value .when displayed is rounded to p decimals and printed right justified in the
first of w columns
The negative numbers will be printed with a minus sign
The default precisions is 6 decimal places
%w.p.c
It takes the form [-] m .nnnne{+/-}xx
Padding the loading blanks with zeros and printed with left-justified is done by
introducing a zero or minus before the field width specifier
Some system supports runtime field specification
Printf (“%*.*f”,width ,percioucs ,number );
Both field width and percious are given as argunments
Printf (“%*.*f”.7,2 number);
Both field width and percious are given as argunments
Printf (“%*.*f”,7.2 number);
Is equivanlent to printf (%7.2f”number);
Format output
Printf(:%7.4 f”,y) 98.7654
Printf(“% 7.2 f”,y) 98.77
Printf (“%72”,y) 98.77
Printing a single charcter
A single charcter can be displayed in a desired position by using the format
%wc
Charcter will be displayed right justification in the field w columns
The default value for w is 1 (one)
PRINTING OF STRING
Syntax
%w.ps
Where w specifies the field width for display and p instructs that only the first p charcter of
strings are displayed the display is right justified
CONTROL STATEMENT:
C language processes some decision making capabilities and support the following statement
knowns as control or decision making statement
If statement
Switch statement
Conditional operartor
Goto statement
DECISION MAKING WITH IF STATEMENT
The if statement is a powerful decision making statement
It is used to control the flow of execution of statement
If it is two ways decision making statement and it is used in conjunction with an
expression
SYNTAX
If (test.expression)
It allows the computer to calculate the first once then depending on the value of the
expression it transfer the control to a particular statement
Test expression has two parts to follow one true condition and the other for the false
condition
SIMPLE IF STATEMENT
SYNTAX
If (test expression)
{
Statement_blocks:
}
Statement _x ;
Statement_ block may be a single statement or a group of statement
If the test expression is true the statement blocks will be executed
If the test expression is false the statement block will be skipped and the execution
jump into to the statement x
When the condition is true both the statement blocks and the statement—x are
executed is sequence
The program tests the type of category of the student if the student belongs to the
sports category then additional bonus marks are added to the marks
IF..ELSE STATEMENT
Syntax
If test (expression)
{
True-block statement
}
Else
{
False-block statement
}
Statement -x;
If the test expression is true ,then the statement are executed
Otherwise,false blocks statements are expressed
In either case,either true -blocks or false -blocks will be executed not both
In both cases the control is transferred subsequently to statement -x
Ex:
Counting the number of girls and boys in the class
For boys code=1
For girls code=2
If (code==1)
Boy=boy+1;
Else
Girl =girl+1;
Statement -x ;
If the code is equal to 1,the statement boy=boy+1 is executed and the control is
transferred to statement -x after skipping the else part
If the code is not equal to 1 the statement boy= boy+1 is skipped and the else part
girls =girls in 1+1 is executed before the control reaches the statement
NESTED IF-ELSE STATEMENT
When a series of decisions are involved more than one if else statement is used
If the condition 1 is false the statement -3 will be executed ;otherwise it continues to
perform the second test
If the condtion-2 is true the statement-1 will be evaluated otherwise the statement -2
will be evaluated and then the control is transferred to the statement x
EX :
If (gender==”f”
{
If (bal>5000)
Bonus=0.05*sal;
Else
Bonus =0.02*sal;
}
Else
{
Bonus =0.02*sal;
}
Sal=sal =bonus :
ELSE IF LADDER
C also permits decisions statements a multiple decisions is a chain of its in
which the statement associated with each else is an if
SYNTAX
If (condition-1)
Statement -1;
Else if (condition-2)
Statement -2
Else if (condition 3)
Statement-3;
Else if (condition )
Statement -n;
Else
Default statement
Statement-x;
This is known as else if ladder the condition are evaluated from the top to down if say one
conditions is true the statement asscicated with its executed and then the control is transferred
to the statement x remaining statement is skipped when all the condition becomes false then
the final else containing default statement will be executed
SWITCH STATEMENT
C has a built in multi way decision statement known as switch
Switch statement tests the value of a given variable against a list of case values and
when a match is found a block of statement associcated with that case is executed
Syntax
Switch (expression)
{
Case value -1;
Block-1;
Break ;
Case value -2 ;
Block -2;
Break;
Default
Default- block
Break;
}
The expression is an interger expression or charcter
Value -1,value-2 are constants or contants expression are known as case labels
Each of these labels should be unique
Block-1 ,block-2 , are statement lists and contains zero or more statement
Case labels ended with a color (:)
When the switch is executed value of expression is successively compared against
values value – 1 value – 2
If the case is found whose value matches with value of the expreesion then the block
of statement follows the case are executed
The blocks statement at the end blocks signals at the end of a particular case and an
exit from the switch statement transferring the control to the statement following the
switch
The default is an optional case when it is will be executed if the value of the
expression does not match with any of the case values
If it is not present no action takes of all the matches fail and the control the
transfeered statement -x
The selection process of switch statement is shown in the figure
Ex
Switch( index)
{
Case a:
Grade=’A’;
Break;
Case b:
Grade=’B’;
Break;
Case c:
Grade =’C’;
Break ;
Default :
Grade=”fail”;
Break;
}
Printf(“%s\n”,grade);
GOTO STATEMENT
C support the goto statement to branch unconditionally from one point tp another in
the pogram
The goto requires a label in order to identify the place where the branch is to be made
A label in any valid variable name and must followed by colon
The label is placed immediartely before the statement where the control is to be
transferred
The label can be placed anywhere in the program either before or after the goto label
statement
Two types if goto statement
*forward jump
* backward jump
Syntax for forward jump
goto label;
----
-----
Label:
Statement ;
Syntax for backward jump
Label:
Statement;
--
--
--
Goto label;
Go to breaks the normal sequential execution of the program
If the label is before the statement goto label;a loop will be formed and some
statement will be executed repeadtly this is known as a backward jump
If the label : is placed after the goto label; some statement will be skipped one the
jump is known as a forward jump
Ex
Main()
{
Double x,y;
Read;
Scanf(“%f”,&x);
If (x<0)goto read;
Y=sqrt(x);
Printf (“%f%f”,x,y);
Goto read;
}
This program uses two goto statement
The(2) goto statement after printing the x to transfer the control back to the input
statement and the other to skip any futjer compound when the number is negative
Due to unconditional goto the statement at the end the control is always transferred
back to the input statement
ITERATION STATEMENT
Iteration statement are also known an loops allows a set of instruction to be performed
until a certain condition becomes false
The condition may be predefined or open ended
The loop strcture avaible in ‘C’one
.. the while loop
.. the do.. while loop
.. the for loop
In looping a sequences of statement are executed until sources condition for
terminiation of the loop are stasified
A program loop consist of two segements one known as the body of the loop and the
other known ad the control statement
The control statement tests certain condition and then directs the repeated executions
of the statement contained in the body of the loop
Depending upon the position of the control statement in the loop a control strcture
may be classified as the entry- controllec loop or exit – controlled loop
ENTRY CONTROLLED LOOP :
The control statement are test before the starts of the loop execution
If the condition are not satisfied then the body of the loop will be executed
EXIT CONTROLLED LOOP:
The test is performed at the end of the loop and therefore the body is executed
uncodtionally for the first time
WHILE STATEMENT
While statement is used to carry out looping operations in which a group is statement
is executed repeadtly until some condition has been stasfied
Syntax
While (test condtion)
{
Body of the loop
}
While is an entry – controlled loop statement
The process of repeated executions of the body contuines until the test = condition
finally becomes false and the control is transferred of the loop
On exit the program continue with the statement immedieatly after the body of the
loop
The body of the loop may have one or more statement
Braces are needed only if the body contains two or more statement
Ex
Main()
{
Int digit =0;
While digit =0;
While (digit <=9)
{
Printf (“%d\n”.digit );
++ digit :
}
}
Output
0
1
2
3
4
5
6
7
8
9
THE DO WHILE STATEMENT
The do.. while loop is sometimes refreed as do ..loop in c
This loop checks its conditions at the end of the loop
This means that do.. while loop will be execute at least onceeven if is the condition is
false intialltly
SYNTAX
Do
{
Body of the loop
} while ( test – condition);
At the end of the loop tge test condition in the while statement is evaluated
If the condition is true the program continues to evaluates the body of the loop once
again
This process continues as long as the condition is true
When the condition between false the loop will be terminated and the control goes to
the statement that appears immediatetly after the while statement
Since the test -condition is evaluated at the bottom of the loop the do while constructs
provide an exit – controlled loop
Ex
Main()
{
Int digit =0;
D0
{
Printf ( “%d\n”,digit );
++ digit ;
}
While ( digit <=9);
}
The printf statement is executed first among the value of the digit is incremented by
value
The body of the loop is always executed at least once
FOR LOOP STATEMENT
For loop is entry controlled loop provides a more concise loop control strcture
Syntax
For (initialization – condition increment )
{
Body of fhe loop
}
The execution of for statement is as follows
Intiallization of the control variables is done first using assignment statement
A values of the control variable is tested using the text condition the test condition is a
relational expressions determines when the loop will exit
If the condition is true the body of the loop is executed otherwise the loop is
terminated and the execution continues with the statement that the immediuatetly
follows the loop
When the body of the loop is executed the control is transferred back to the foe
statement after the evaluating the last statement in the loop if the conition
Is stasified the body of the loop is again executed this process continues till the value
of the control variable fails to satisfy the test condition
Ex:1(incrementing)
For (x=0<=9 ;x-x+1 )
{
Printf (“%d”,x);
}
This loop allows negative increments this above loop will be executed for 10 times
and prints value 9to 0 in one line
Additional features of for loop
1) More than one variable can be initialized at a time in the for statement
Ex
P==1;
For(n=0;n<17;++n)
Can be rewritten as
For (p=1 n=0 ;<17 ;++n)
2 the increment section may also have more one part
Ex
For (n=1;m=50;n=<17;++n)
2 the increment section may also have more one part
Ex
For ( n=1 ;,m=50 ;<m;n+1,m=m+1)
{
P=m/n;
Printf (“%d%d%d”,n,m,p);
}
Note
Multiple argunments in the increment section and intiallization section will
be seprated by comma
3 the last condition in the loop may be compound relation
Ex
Sum =0;
For(i=I;<20&&sum <100;++i)
{
Sum=sum +1;
Printf (“%d%d “,sum ,i);
}
NESTING OF FOR LOOPS
One for statement with in another for statement is allowed in c
The nesting may contains up to 15 levels many compliers allow more than 15
Ex
M=5 :
For(i=1;i<=16;i++)
{
Sum=i*m;
Printf (“%d%d%d”I”*”m”=”sum);
}
UNCONDITIONAL TRANSFER STATEMENT
C performs as unconditional branch
Goto
Break
Continue
Unconditional branching means “transfer control from the point where it is specified
statement
Go to can be used anywhere in the program where break and continue statements are
conjunctions with any of the loop statement
BREAK STATEMENT
The break statement can be used to terminate a case in the switch statement and to
foree immediate of loop bypassing normal loop condtional test
When the break statement is encourtred inside a loop the loop immediately terminated
and the program control passive to the statement following the loop
Syntax
Break
Ex
For (i=1<=5;i++)
{
----
----
Break ;
}
CONTINUE STATEMENT :
The contitune statement causes the next iteration of the enclosing loop to begin
When this statement is encourted in the program the remaining statement in thebody
of the loop are skipped and the control is passed to the re – initialization stop
Continue directs the loop to increments portion of the loop and then condtional test
Syntax
Continue
EXIT () FUNCTIONS
Used to terminates a program just break statement is used to terminate a loop a return
statement is used to terminates a function
Exit () function is used to terminate the program and return control to the operating
Exit function is of two types
Exit (0)
Exit(1)
Exit(0) is called by the user for a successful termination of an instruction
Exit(1)is called terminate a program in case of an error
