Perl Tutorial - 30: Nested Loops Video Lecture | Perl Building Blocks: An Introduction to Perl - Back-End Programming

hello guys welcome to my channel this is
the third year to doll in this course
and this at all we will be talking about
nested loops in Perl so we're gonna
follow a slightly different approach in
this tutorial you know instead of just
looking at what we're doing in the
script we're going to start with a
problem statement so let's say you want
to write a script that produces the
following output you want to see a
pattern of asterisks and you want to see
five aspects on the first line
four on the second three on the third
two on the fourth and one on the fifth
line and you want to do this using loops
or you know anything that you see fit
that we learned till now in this course
and you know trust me you can do this
only through loops so you know it's
clear to us that since we want five rows
of output we would have to use some loop
that would give us the Liberty to have
you know a pattern of asterisks on five
different lines and you know we could
achieve this using a simple while loop
so we need five iterations and for that
the code is very simple we need a
control variable for the loop first of
all so for that I have created a scalar
variable a which has the value five and
I've done this on line number three in
this script called nested underscore
loops and then on line number five I
have the keyword vile and my test
condition is while a is greater than
zero so a initially has a value of five
and we are testing for a and zero so you
know it's quite clear since we want five
iterations we are going to decrement the
value of a or reduce the value of a by
one in each iteration of the loop and we
are doing that here on line number 13 we
are reducing the value of a and also
since we want the cursor to be on a new
line for every iteration of this outer
loop we are also printing a new line
escape sequence so you know this is
actually you know I'm going to print the
new line escape sequence but it's just
going to shift the cursor to the new
line so that we can print the pattern of
stars on fresh line for every iteration
of the outer loop so since this loop is
you know the main loop we call it the
outer loop and since you know the loop
that I have on line number eight is
within this loop we call this the inner
loop right and now that we have taken
care of the first part of the problem
which is to have output on five
different lines we now have to do
something that prints five asterisks on
the first line four on the second three
on the third so on and so forth right so
for that we're going to use another loop
and the control variable for that is
going to be called B and it initially
has a value of one and we're going to
check while the value of B is less than
or equal to a so remember a initially
has the value of five if B would have
one then if you are checking while B is
less than or equal to a this loop itself
is going to have five iterations in the
first iteration of the outer loop and
you know for the first iteration of the
outer loop we are going to have five
astrick symbols because as I said this
one's going to have five iterations and
we are updating the value of B here
instead of decrementing it which we were
doing in the case of a and in the second
iteration is going to have the value for
B is going to have the value 1 so this
loop the inner loop is going to have 4i
tration so we will have four asterisks
so on and so forth we'll have the
pattern that we want so let me save this
file and run it to show you the output
and there we go we get the exact pattern
that we wanted to print five Asterix for
Asterix three two and one so and so
forth that's what we had to do and in
Perl you could nest a for loop inside a
while loop a while loop inside a for
loop or do-while loop inside a for each
or you know for each inside while you
could play with loops as much as you
want and you could have as many loops
within loops there is no limit on how
deep the structure can be but as you
increase the number of loops in your
script the code becomes complicated it
becomes hard to manage so you need to
if you use the minimum number of loops
as possible so that your code is
manageable and you know you can make
modifications to it if required
you know conveniently so that's it for
this video I hope you guys had fun
watching this one you may subscribe to
my channel if you haven't already I'm
going to see you in the next video till
then take care