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#17 While Loop in Java — Transcript

by Telusko · 2,570 words · 321 segments · language en · Watch on YouTube

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0:00so in the last video we have talked
0:01about the need for Loops right and so we
0:04have decided that if you want to repeat
0:06something Loops can be a good thing and
0:09we also talked about there are different
0:10types of Loops right we have while loop
0:12do while loop for Loop in this video
0:13let's try to understand the first Loop
0:15which is while loop so we'll go over
0:18this go for the same statement here if
0:19you can see we are Printing High and
0:21again as I mentioned before ignore this
0:23x this is a suggestion given by your vs
0:25code uh this is what we are typing just
0:28high and what I want to do is I want to
0:30print this High multiple times so what
0:34we can do is we uh we can say Hey you
0:36know Java I want to print this multiple
0:39times Java will say okay
0:41the first thing you do is you put this
0:43in a block of course it's not compulsory
0:45when you have one statement but just to
0:47understand just to get started we are
0:48putting that in a block now and then of
0:51course we have to follow into
0:51indentation as well and we are doing
0:53that now what we can do is we can say
0:55Hey you know Java I want to run this
0:58five times so Java will say okay if you
1:01want to repeat you have to use a keyword
1:03called while now in English as well we
1:06normally use while to say repeat
1:08something or while it is true do that so
1:11here we can say while it is what in this
1:15bracket you have to mention is it true
1:17or false now basically that's how Wild
1:19works so if you say true it basically it
1:22will just keep printing this High
1:24because we are saying true it says okay
1:26while I'm true I will keep printing it
1:28so that's why if you just run this code
1:30by just by mentioning the
1:33while
1:35you can see we are getting high I just
1:37kept printing okay it's it's not
1:39stopping if you can see if I try to
1:40scroll down it is continuously happening
1:43and maybe it will uh fill my Ram it will
1:47crash okay I don't think so but let me
1:49stop this execution otherwise there will
1:51be an issue so what we can do is I don't
1:53want to continuous this for a long time
1:56I want to do that for a particular
1:58condition maybe I want to say I want a
2:01counter which will start from one and it
2:03will stop at five oh when I say counter
2:06it means I need a variable well I can
2:08store the value so what we can do is
2:10here I can just come up and I can say
2:12int I is equal to let's say one now most
2:16of the time when you use Loops you will
2:17be using a variable name I it's not
2:20compensative we can use any variable
2:21name but it makes sense right because
2:23normally when you go inside the while
2:26you are executing something you are
2:28changing the values of the eye
2:31you basically increment it right so it
2:34makes sense to call it as a iterator
2:35which will iterate so I iterator makes
2:39sense and that's why most of the time
2:40you say i j but as I mentioned you can
2:43use any variable of your choice so we
2:45are using I here which is I is equal to
2:471 and then what we can do is every time
2:51you run this loop after Printing High
2:53you can just increment the value of I
2:56oh but then how do we increment and we
2:58have seen that right we have a concept
3:00of I plus plus so I plus plus will
3:02simply increment the value of I okay
3:05that makes sense and oh how do I check
3:10for the condition see it makes sense now
3:12because I is 1 and every time you run
3:15this Loop the in the I value will
3:16increase right so if you run this while
3:18for let's say five times it will
3:20increment the value of I let me show you
3:23what I will do is I will print hi as
3:25well as I will print uh maybe you can
3:28you can print both the things I say on
3:30the same line you just have to give a
3:32space after high and I can give a plus
3:34symbol so when you want to concatenate
3:36two different things High and a number
3:39we can use a plus operator yeah plus
3:41Works in that way it works for addition
3:44as well as it works to concatenate two
3:46things
3:47and here I'm writing I now let's see
3:51what's the output is again I have not
3:52changed the condition so it will print
3:54infinite times
3:55but I just want to see what happens if I
3:57compile this code
3:59and run you can see the value of I is
4:02incrementing continuously
4:04and you can see it so fast depend upon
4:06your machine speed as well and let me
4:07know when you try on your machine how
4:10fast it is so what I want to do is I
4:12want to stop this somewhere so we have
4:14to apply a condition how do I stop it so
4:16we have to say if I is less than equal
4:19to 4 so what it will do is it will check
4:22for the condition remember we have
4:23talked about this in relational
4:24operators it will continuously check for
4:27the condition so what how it runs is
4:29initially it will set the value of i as
4:311 and then in the while loop it will
4:33check if the value of I which is 1 is
4:37less than 4 yes it will continue it will
4:40go inside the loop it will print high it
4:43will also print the number which is 1
4:45and then it will increment the value of
4:47I what next it will go back to while
4:50loop because and again it will check for
4:52the condition because that's a while
4:53right it will continuously happening it
4:55will again check for the condition where
4:57it says okay I value now it's 2 so 2 is
5:00less than 4 yes and it will continue at
5:02the end when the I value becomes 4 it
5:06will check 4 is less than equal to 4 yes
5:08it will print High and 4 as well so we
5:10got four iterations and then it will
5:13increment the value of I which is it
5:15will make it five it will go back here
5:18and it will check is 5 less than equal
5:21to 4 false and that's where it will jump
5:24out of the loop so remember this thing
5:27the moment your while gets a false here
5:29it will not execute this block cool
5:31right now after saying all those things
5:33let's try to compile and run and you can
5:36see we got high one high two High three
5:38and high four that's how while loop
5:40works now with this I have a question
5:42for everyone here and the question is
5:44what if at the end I'm just saying as
5:48out and I'm saying buy and with this by
5:52I'm printing the value of I what do you
5:53think what will be the output of I
5:55okay try to guess it I'm just running
5:57this code to show you the output compile
6:00run you can see we got all the values
6:02here but with by you got five you know
6:05why is because
6:07we got false here when the value of I is
6:115 and that's why you got the value here
6:14now since I is declared outside the loop
6:17the value will be maintained okay now
6:20one more thing here I want to run this
6:22in a debug mode let me show you how it
6:23works in debug mode so what I can do is
6:25I can go to run
6:27and I can say start debugging okay so
6:30there are some options okay for
6:31debugging you have to basically you know
6:33uh you have to set the checkpoints what
6:36I will do is I will just set the
6:37checkpoint here so basically debug is an
6:40awesome feature in programming where you
6:42can set the checkpoint this is where you
6:44want to iterate one by one so normally
6:46when you run the code it will directly
6:48give all the output right what if you
6:50want to see the steps so it makes sense
6:52let me just clear this and again I will
6:54go into run
6:55and get into the debug mode okay so you
6:58can see uh we are in debug mode now and
7:02here on the left hand side we got
7:03variables we got local a and I we have
7:06two variables you know why we got a is
7:08because of this a variable here but it
7:10is at this point we want to ignore that
7:11we want to focus only on I variable and
7:14the value of I at this point is one you
7:17can see that I is one but now if I say
7:21step into you can see we got
7:23system.winder it will print the I and I
7:25the value of I which is one uh okay I
7:28want to go step into now it will
7:30increment the value of I you can see we
7:32got the output as well we got high one
7:34and then when I say step over it will go
7:38for the next step and you can see before
7:40executing it the value of I is 1 but
7:42once I execute that statement the value
7:44of I now becomes 2 okay so that it went
7:47back to while loop and this will keep
7:49happening for I value 2 I value 3 I
7:52value 4 as well the moment your value of
7:55I because comes 5 here you can see the
7:57value of I is 5 now it is checking and
7:59it falls it it will jump out of the loop
8:02it will print by with the value 5. so
8:05that's how your while loop Works in fact
8:07what you can also do is we can run a
8:10nested Loop here now how an estate Loop
8:12looks looks like let's say I want to
8:14print i1 and then I want to do something
8:17else maybe I want to print hello three
8:20times after every high so let's say I'm
8:23Printing High here and then I want to
8:25print hello as well
8:26and I don't want to print the value of I
8:28anymore
8:29or maybe let's print the value of I
8:30let's see what happens if you keep the
8:32value of I here and then incrementing it
8:35here as well that makes sense but now
8:37what I want to do is I want to
8:40after printing this High I want to print
8:42hello five or three times now in that
8:44case I can simply say hello and I can
8:47write the same statement multiple times
8:48right that's how the loop works right so
8:51I will say hello hello and you can see
8:53we got hello three times but don't you
8:55think we are doing the same thing
8:56multiple times so it makes sense to put
9:00that in a loop so I can simply say while
9:03oh but what should be the condition can
9:06I say I is less than equal to 3 no right
9:09because see I want this hello three
9:12times for every high so high we are
9:15getting to four times and for every High
9:17I want Hello three times
9:20so the same value will not work in that
9:22case what you have to do is you need to
9:24work with a different variable and I
9:27will create one more variable here which
9:28is called J and the value of J initially
9:30will be 1
9:31and then every time you execute this
9:34while loop where it prints High
9:36it will jump inside here it will set the
9:39value of J as 1 it will set the value it
9:41will check for the condition where J
9:43should be less than equal to
9:453 and then every time you do that let me
9:48open the curly brackets
9:50and we can put this hello statement in
9:53here so we don't have to put this thing
9:56now I can just simply say hello and of
9:59course I want to print J plus plus as
10:01well and remember this thing we are
10:04saying J plus plus in the inner while
10:06loop and then we are saying the I plus
10:09plus in the outer loop okay if you want
10:12to understand this with an analogy uh
10:15just go with an example of days in a
10:18week so we have multiple days in a week
10:20right so we have Sunday Monday Tuesday
10:21Wednesday Thursday Friday Saturday
10:23Sunday I've already mentioned you know
10:26we we basically want Sunday twice a week
10:29but anyway so if we talk about these
10:30days every day we have 24 hours right so
10:33if you say this is 1 pm on Monday again
10:36the Monday gets over the clock will
10:38start at zero right then zero one two
10:40three four five six and then it
10:42continues right as the date changes the
10:45clock repeats in the same way once your
10:47eye is incrementing it's like a days
10:49Monday Tuesday the inner loop you can
10:52imagine that's as a number of hours it
10:54will keep incrementing but after three
10:56it will go back to one because it will
10:58complete the inner loop it will go back
11:00to Outer Loop and again again the value
11:02of J will become one let me show you how
11:04it works let me just compile this code
11:06compile and
11:09run you can see we got high uh we are
11:12still printing one here you know what I
11:14will do I will also print J so that you
11:16can see the value of J as incrementing
11:19it
11:20and let me give a space here as well let
11:22me say clear
11:24compile run so you can see we got high
11:27one and then it is going for the inner
11:29loop now so once you execute this High
11:31it will go for the inner loop where we
11:33are saying J is less than 3 so basically
11:36it will print this statement three times
11:38because the value of J is less than
11:41equal to 3 so it will iterate three
11:42times
11:43and then again you have to go for the
11:45outer loop so the the moment this is
11:47false it will execute I plus plus where
11:49it will make I2 it will go back to the
11:52upper loop again it will say okay now
11:55the value of I is 2 is 2 less than equal
11:58to 4 yes it will go inside it will print
12:01the value of high which is high 2.
12:04again it will make the value of J as 1
12:06and that's why it is incrementing again
12:10cool right so this is basically called a
12:13nested while loop so that's it from this
12:16video where we have talked about uh how
12:19to create a while loop how to use a
12:21nested Loops using uh while loop so I
12:24hope you enjoyed in the next video we'll
12:26talk about do while loop

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