Part 14 - C# Tutorial - do while loop in c# Video Lecture - C sharp Enhance

hello welcome to presume technologies
I'm venket this is part 14 loops in c
sharp in this session we will be talking
about do-while loop in part 13 we
actually spoke about while loop and in
later sessions we'll talk about 4 and
for each loop let's look at an example
in part 18 when we are talking about a
while loop we wrote a simple program
where the program will ask the user user
to enter a target number and then
program will continue to plan the even
numbers until that target number using
the while loop if you're not sure of how
to use while loop please check part 13
in this video series okay let's rewrite
that program and then we will enhance
that using a do-while loop so console
dot write line so let's ask the user to
enter his target number so please enter
your target so once the user enters his
target we need to read that from the
console and store it in a variable so
let's read it from the console using
console to read line and we have to
convert that to an integer so we use
into the parse method so we have to use
a target number and we need to start
counting at zero so start equals zero
and reviews the while loop while start
is less than or equal to user target
what we need to do we need to plant that
even number so control dot right and
between each event number we want a
space we will give that space and then
we need to increment the start counter
by two because we want to print even
numbers now this program is very much
similar it's actually exactly same to
what we have seen in while loop video
session so if you're not sure if you
need explanation about this program
please
check back that tutorial all right so
what will this program do it will ask
the user to enter a target and it prints
even numbers until this target now I
want to make this program little more
interactive and since this program will
run only once now if I have to print
let's say even numbers into 20 I have to
close this program and run it once again
so every time I want a different set of
even numbers I have to run the program
again so but I want the user to be in a
position to decide when he wants to stop
printing even numbers ok he wants to
continue you know with the program as
long as he wants it ok and then when he
decides okay I don't want to print even
numbers anymore I want to print the
program that's when it should print
that's when it should actually quit ok
to do that we will ask the user ok do
you want to continue do you want to
continue and the two options he has a
yes or no now the user will say yes or
no so we need to read that option from
the console so read the user choice from
the console and store it in a variable
since yes or no is a string we will
create a variable of type string string
user choice equal to consult or treat
line so once we have the user choice so
we are expecting from the user only yes
or no words if he types anything else
apart from yes or no it's a garbage we
don't know what to do so we have to ask
him once again to enter a valid you know
choice yes or no okay so if user choice
is not equal to yes and if use a choice
not equal to
now if the user choice is not yes and if
it is not now then we know that it's an
invalid input so console dot readline
invalid choice please say yes or now
okay so how long we want to do execute
these four statement as long as he
enters yes or no if he enters anything
about from those two then we want to
keep this happening and we want to
prompt keep prompting the user now your
input is invalid please enter yes or no
and to do that we have to use some kind
of a loop so we can make use of actually
the do-while loop so we want to do this
we want to do all this
until do-while how long we should do as
long as the user choice is not equal to
yes and not equal to now if it's not any
of these you know keep prompting the
user to enter a valid input but here we
have an error says user choice does not
exist in the current context that's
because we declared a user choice
variable within the do loop so the scope
is not available here so we should
actually declare that variable right
there and initialize that with an empty
string so we have declared it there
there is no need to actually I'm sorry
to actually declare it here so let's
delete that so if you look at this one
it's a very simple piece of code we are
using a do-while loop here okay do
continue to execute all these statements
as long as this condition is true as
long as the user has not entered s and
now prompt him okay please enter a valid
choice
alright okay so now then we actually go
ahead and run this program look at
what's going to happen so it's asking me
please enter your target let's say ten
it prints them to ten and it's asking me
do you want to continue let's say I type
some garbage here it says invalid choice
please say yes or no do you want to
continue again I take the garbage so it
is now it's now in this loop as long as
I type yes or no it doesn't get out of
that loop
but the moment I type yes let's say the
program will terminate now because after
this there's nothing it's just losing
race in the program terminates okay but
what should ideally happen it should ask
me to enter my target once again so even
this piece should be in a loop until he
decides okay I don't want to run this
program anymore okay so let's have
another block of two while loop so do
all this do all the stuff okay
but how long while the user choice it
says as long as user says okay yes I
want to continue yes I want to continue
you know continue doing it so while user
choice is equal to yes but again we have
a problem here you can see that let's
put a semicolon there you can see that
there is a red squiggly line the name
user choice does not exist the current
context user choice is declared here but
we are using outside of the do loop so
we need to declare it at the beginning
so string user choice instead of using
empty strings we can also use a property
like so string empty okay so that's it
so now if we go ahead and run this
program
okay let's not create to enter my target
let's say I want to print even numbers
until 5 0 to hold do you want to
continue I type some garbage in it says
invalid choice please say yes or no so I
say yes please enter your target this
time I want to say let you know I want
to print even numbers until then it
prints even numbers until then again
it's asking me do you want to continue
now I say no please enter any key to
continue and the program terminates okay
however there is a small error with this
program let's look at that and I'll end
this program it's asking me enter you
target let's say 5 do you want to
continue now let's say I type in yes all
capital letters can look at what's going
to happen
saying invalid choice you know why that
happens that's because of a case
mismatch it's asking me do you want to
continue and I have typed yes ok so use
the choice you'll actually receive that
yes because we are reading from the
console and then is capital letter y es
equal to this one obviously now it's not
equal to that okay so what's going to
happen it becomes true and it is also
not equal to no it enters here and says
you know invalid choice so in order to
overcome that issue what you can do is
convert whatever the user has entered
into an uppercase and compare so now
whatever the case may be upper lower or
a mix of both it's still going to work
the total issues so if we run it now
please any target I want to print until
10 do you want to continue small Y
capital e small s and still o invalid
choice please say yes or no it shouldn't
be doing that
let's debug why it's happening okay so
we said user choice control the treeline
the two upper can we are reading
whatever the user has entered and
converting that to upper yes and that's
obviously because you're comparing it to
small letters here so make that above
and make this as well because we
converted the user choice to upper but
we were comparing it to Capital y and
smaller case e and s okay so now the
program should work without any issues
so then we want to continue our now
small y capital e small s but still it
should work do you want to continue yes
or no small Y capital s oh yeah and we
have to do all that here as well I just
did it in one place so we need to do it
to all places in order for that to work
as expected right so let's go ahead and
run that ten do you want to continue
small Y capital e small as it should
work this time please enter your target
so for do you want to continue both of
them small press any key to continue so
it works okay so we can very easily
create loops like this using a do-while
loop if you actually remember part 12
and on switch statement continuation we
have actually written a small you know
coffee purchasing program where we have
created a loop similar to this but we
haven't used do-while loops there we
used go-to statement and by all means go
to statement should actually be avoided
because when we use go-to statements you
know the control randomly jumps from one
location to another location and in the
program is a little complex one it
becomes extremely difficult
debugging that application that's why
it's always recommended to avoid go to
statement and most of the time we can
actually in fact the coffee purchasing
program that we have created using go-to
statement you know we can relate that
using do-while loop if you're not sure
what that coffee purchasing program is
and if you need explanation of that cool
please check back you know part 12 of
this video series okay but however I
have that piece of code here for you I
will quickly walk you through the
program so this coffee purchasing
program so if you look at this program
I'll you know it's it's using labels
here if you're not sure what the label
is and how to use go-to statement as it
will you please check back part well and
then we have a decide label there and
look at this they're using go to decide
go to specific label and similarly
somewhere we say go to start okay so but
this go-to statement should be avoided
by all means so let's run this program
so please select your coffee size one
for small two for medium three for large
let's say I want to buy a large coffee
okay I've got one large coffee but do
you want to buy another coffee let's say
I want to buy another coffee another
large one we want to buy another coffee
now so I bought two two large coffee and
my bill amount is six so this program
isn't some kind of a loop just like the
one we have written you know prior to
this okay but I have rewritten the same
program using do-while loop
so now let's copy-paste that let's run
this ok please select your coffee size
let's say I want to buy a large coffee
we want to buy another coffee Acer know
I'm typing in garbage so it says your
choice is invalid please try again do
you want to buy another coffee yes or no
let's say yes and let's enter the large
size so do you want to buy another
coffee now look at this got two large
coffee and the bill amount is six the
behavior is exactly the same but instead
of using go to statement this time I'm
actually using a do-while loop just like
how we have used it in even numbers
program ok so many at times you can
actually avoid using go to step so if
error if it's possible to do so you know
always consider replacing go-to with
other loops alright
so that's about do-while loop so in the
previous session we actually spoke about
while loop and if you remember while
loop checks the condition at the first
at the beginning if the condition is
satisfied then the statements following
the while loop are executed within the
while loop block are executed and this
process is continued as long as the
condition evaluates to true the moment
the boolean expression for the while
loop becomes false the the block is kept
and then the statement following the
while loop is executed ok when we use
any of these loops it's always important
to keep in mind to update the variable
that participates in the boolean
expression so that the loop can end at
some point of time whereas in the
do-while loop it do loop checks its
condition at the end of the loop ok so
this means the do loop is guaranteed to
execute at least once and usually do
loops are used to present a menu to the
user for example something like do you
want to continue yes or no what kind of
coffee do you want to buy one for small
two for large three four - four medium
three for large okay so if you want to
present the menu to the user and then
based on that menu we want to take any
decisions then probably we can make use
of this too
okay so if you look at the differences
between while and do-while loop while
loop checks the condition of the big in
angle is two while loop checks the
condition at the end of the loop and
because of this difference you know the
do loop is guaranteed to execute at
least once whereas while loop there is
no such guarantee if the condition
becomes false the first time it doesn't
even execute once okay so do loop is
guaranteed to execute at least once
whereas while loop is on so that's it
for today thank you for listening have a
great day