Loops
The versatility of computer lies in its ability to perform as
set of instructions repeatedly. This involves a repeating some
position of a program either a specified number of a time or
until a particular condition is being satisfied. This repeative
operation is done through a loop control structure.
There are 3 methods by way of which we can repeat a part of a
program. They are
- Using a while statement
- Using a do while statement
- Using a for while statement
While loop: It is a conditional control loop statement
The while is an entry controlled loop statement. In entry
controlled loop, the control conditions are tested before start
of the loop execution. If the conditions are not satisfied then
the body of the loop will not be executed.
General form
While (test condition) { Body of the loop }
The condition
being tested may use relational or logical operators.
Eg:
program to print "n" natural numbers while using loop.
main()
{
int n, i=1;
clrscr ();
printf ("enter the values of n");
scanf ("%d", &n);
printf ("natural numbers from 1 to %d ", n);
while (i<=n)
{
printf ("%d\ t", i);
i++;
}
getch ();
}
Eg: program to display even numbers &odd numbers
from 1 to n
void main ()
{
int n, i=1;
clrscr();
printf("enter the values of n");
scanf("%d", &n);
printf("even numbers from 1 to %d ", n);
while(i<=n)
{
if(i%2==0)
printf("%d \t", i);
i++;
}
printf("odd numbers from 1to %d ", n);
i=1;
while(i<=n)
{
if(i%2==1)
printf("%d\t", i);
i++;
}
getch();
}
do while
On some occasions it might be necessary to execute the body of
the loop before test is performed. Such situations can be
handled with the help of do while statement.
General form:
do
{
Body of the loop
} while (test condition);
On reaching the do statement the program proceeds to evaluate
the body of the loop first. At the end of loop, the test
condition in the while statement is evaluated. If the condition
is true, the program continues to evaluate the body of loop once
again. This program continues as long as the condition is true.
When the condition becomes false, the loop while be terminated
and the control goes to the statement that appears immediately
after while statement.
Since, the test condition is
evaluated at the bottom of the loop,the do while construct
provides an exit-controlled loop and the form the body of the
loop is always executed at least once.
Flow chart for
exit control:
Example: To print ‘n’
natural number using do while
#include < stdio.h>
#include < conio.h>
void main()
{
int n,i=1;
clrscr();
printf("enter any number");
scanf("%d",&n);
printf("natural numbers from 1 to %d",n);
do
{
printf("%d\t",i);
i++;
}while(i<=n);
getch();
}
FOR Loop
The for loop is another entry controlled loop that provides a
more concise loop control structure.
The general form of for
loop is
for(initialization; test condition; increment)
{
Body of the loop
}
1.The initializing control
variables using assignment statement such as i=1&count=0,we
can initialize control variables. The variables i & count
are known as
LOOP CONTROL VARIABLES 2. The value of
control is tested using the test condition. The test condition
is a relational expression, such as i<10 determine, when the
loop will exit. If condition is true ,the body will executed
otherwise the execution continues with the statement that
immediately follows the loop.
3. When the body of the loop
is executed, the control is transferred back to for statement
after evaluating the last statement in the loop. Now the control
variable is incremented using assignment statement such as i=i+1
and the new value of control variable is again tested to see
whether the loop condition is satisfied or not.
Ex: To
print 1 to 100 digits
#include < stdio.h>
#include < conio.h>
void main()
{
clrscr();
for(i=1,i<=100,i++)
{
printf("%d/t",i);
}
getch();
}
Ex: To print multiplication table of any numbers from 1
to 20
#include < stdio.h>
#include < conio.h>
void main()
{
int n,i;
clrscr();
printf("enter any number");
scanf("%d",&n);
for(i=1,i<=20,i++)
{
printf("/n%d*d is %d", n,i,n*i);
}
getch();
}