Session 3

DATA INPUT AND OUTPUT
• As we know that any c program is made up of 1 or
more then 1 function.

• Likewise it use some functions for input output
process. The most common function
1) printf()
2) scanf().

printf() Function
• printf() function is use to display something on the
console or to display the value of some variable on
the console.
• The general syntax for printf() function is as
follows
printf(<”format string”>,<list of variables>);

• To print some message on the screen
printf(“God is great”);
This will print message “God is great” on the
screen or console.

printf() Function

• To print the value of some variable on the screen
Integer Variable :
int a=10;
printf(“%d”,a);
Here %d is format string to print some integer value and a
is the integer variable whose value will be printed by
printf() function.
This will print value of a “10” on the screen.

printf() function
• To print multiple variable’s value one can use
printf() function in following way.

int p=1000,n=5;
float r=10.5;
printf(“amount=%d rate=%f year=%d”,p,r,n);

• This will print “amount=1000 rate=10.5 year=5”
on the screen

scanf() Function
• scanf() function is use to read data from
keyboard and to store that data in the variables.
• The general syntax for scanf() function is as
follows.
scanf(“Format String”,&variable);

Here format string is used to define which type
of data it is taking as input.

this format string can be %c for character, %d
for integer variable and %f for float variable.

scanf() Function

scanf(“Format String”,&variable);

• Where as variable the name of memory
location or name of the variable

• and & sign is an operator that tells the
compiler the address of the variable where
we want to store the value.

scanf() Function
• For Integer Variable :
int rollno;
printf(“Enter rollno=”);
scanf(“%d”,&rollno);

Here in scanf() function %d is a format string for
integer variable

and &rollno will give the address of variable
rollno to store the value at variable rollno
location.

scanf() Function
• For Float Variable :
float per;
printf(“Enter Percentage=”);
scanf(“%f”,&per);

• For Character Variable :
char ans;
printf(“Enter answer=”);
scanf(“%c”,&ans);

Single character input – the getchar
function :
• Single characters can be entered into the computer
using the “C” library function getchar.

• In general terms, a reference to the getchar function
is written as.
character variable=getchar();

For example
char c;
c=getchar();

Single character output – The putchar
function
• Single character can be displayed (i.e. written out
of the computer) using the C library function
putchar.
• In general a reference to the putchar function is
written as
putchar (character variable);
For Example
char c=’a’;
putchar(c);

Control Flow In C
• Objectives of the module is

1) How to direct the sequence of execution
using Decision control Structure

2) Have an understanding of the iterative
process using Loop Control Structure

Decision Control Structure
The if-else statement:
• The if-else statement is used to carry out a logical
test and then take one of two possible actions
depending on the outcome of the test

• Thus, in its simplest general form, the statement
can be written.
if(expression)
{
statement;
}

• The general form of an if statement which include the
else clause is
if(expression)
{
statement 1;
}
else
{
statement 2;
}
If the expression is true then statement 1 will be
executed. Otherwise, statement 2 will be executed.

Nested If Else
if<exp1>
{
statement1;
}
else
{
if<exp2>
{
statement2;
}
}

/* Demonstration of if statement */
#include<stdio.h>
void main( )
{
int num ;
printf ( "Enter a number :" ) ;
scanf ( "%d", &num ) ;
if ( num <= 10 )
printf ( “Number is less than 10" ) ;
else
printf(“Number is greater than 10”);
}

Else if ladder
if( expression1 )
statement1;
else if( expression2 )
statement2;
else
statement3;
• For Example
if( age < 18 )
printf("Minor");
else if( age < 65 )
printf("Adult");
else
printf( "Senior Citizen");

• The switch statement:
causes a particular group of statements to
be chosen from several available groups.

• The selection is based upon the current
value of an expression that is included
within a switch statement.

The general form of switch-case
switch(expression)
{
case expression1:
statements;
break;
case expression2:
statements;
break;
case expression3:
statements;
break;
}

• When switch statement is executed the expression is evaluated
and control is transferred directly to the group of statements
whose case labels value matches the value of the expression.
switch(choice)
{
case ‘r’ :
printf(“RED”);
break;
case ‘b’ :
printf(“BLUE”);
break;
default :
printf(“ERROR”);
break;
}

LOOP CONTROL STRUCTURE
• If we want to perform certain action for no of
times or we want to execute same statement or a
group of statement repeatedly then we can use
different type of loop structure available in C.

• Basically there are 3 types of loop structure
available in C
(1) While loop
(2) Do..while
(3) For loop

While Loop
• The while statement is used to carry out
looping operations.
• The general form of the statements
initialization;
while(exp)
{
statement 1;
statement 2;
increment/ decrement;
}

While loop example
#include<stdio.h>
void main ()
{
int digit = 0;
while(digit<=9)
{
printf(“%d n”,digit);
++digit ;
}
}

Do-While Loop
• Sometimes, however, it is desirable to have a loop
with the test for continuation at the end or each
pass.
• This can be accomplished by means of the do-while
statement.
• The general form of do-while statement is
do
{
statement1;
statement2;
increment/decrement operator;
} while(expression);

Do-While Loop Example
#include <stdio.h>
void main()
{
int digit = 0;
do
{
printf(“%d”, digit++);
}while(digit<=9);
}

For Loop
• The for statement is another entry controller
that provides a more concise loop control
structure.

• The general form of the for loop is :

for(initialization; test condition; inc/decrement)
{
statement 1;
statement 2;
}

For loop example
#include<stdio.h>
void main()
{
for(x=0; x<9; x++)
{
printf(“%d”, x);
printf(“n”);
}
}

Reverse For loop
• The for statement allows for negative
increments.
• For example, the loop discussed above can be
written as follows:

for(x=9; x>=0; x--)
{
printf(“%d”,x);
printf(“/n”);
}

BREAK STATEMENT
• The break statement is used to terminate
loops or to exit a switch.

for(i=1; i<=10; i++)
{
if(i==5)
break;
printf(“nI=%d”,i);
}

CONTINUE STATEMENT
• The continue statement is used to skip or to bypass
some step or iteration of looping structure.

for(i=1; i<=10; i++)
{
if(i<5)
continue;
printf(“ni=%d”,i);
}

The output of the above program will be
6,7,8,9,10.

THE GOTO STATEMENT
• The goto statement is used to alter the normal
sequence of program execution by transferring
control to some other part of the program.

• In its general form the goto statement is written
as
goto label;
• Where label is an identifier used to label the
target statement to which control will be
transferred.

goto example
void main()
{
for(i=0;i<5;i++)
{
printf(“i =%d”,i);
if(i==4)
goto stop;
}
stop:
printf_s( "Jumped to stop”);
}

Session 3

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Session 3