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AP Computer Science 1.1 Review of the Basics 315 Views


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Description:

AP Computer Science: Review of the Basics Drill 1, Problem 1. What does this piece of code output?

Language:
English Language

Transcript

00:00

Thank you We sneak And here's your shmoop du jour

00:05

brought to you by loops Have you coming back time

00:09

and time again Little snippet of code for what does

00:13

this piece of code right here what is it output

00:20

on here The potential answers All right here we go

00:29

Pretty simple Request We just have to prove to the

00:33

test and to ourselves that we know how to read

00:35

java code and figure out what it does Well it's

00:38

Not merely a pest problem This kind of thing is

00:41

done all the time when debugging program right but also

00:45

comes up quite a bit when software engineers have to

00:47

maintain or update pulled code Occasionally you'll have to work

00:53

with stuff that had been written five or ten years

00:55

ago or more perhaps by someone who is no longer

00:57

on the project and maybe they didn't leave comments in

01:00

the code so it's tough to figure out exactly what

01:02

it was meant to do or they thought they were

01:05

being really cute and they left their comments and cling

01:08

on Well good luck with that Anyway in this case

01:12

is just eight lines but we can already see that

01:14

there are a couple of loops that end up doing

01:16

an awful lot in that short space So let's go

01:19

through and decode this baby step by step All right

01:23

up top line one sets us up with manager i

01:27

with a value of five Go ahead and write that

01:29

down somewhere Scratch paper in your arms whatever we want

01:33

to keep track of where this variable takes us Line

01:35

two initiates a wild loop which will run as long

01:39

as an injured eye remains greater than zero so it's

01:42

five now and so it looks like we're good to

01:44

go Line three homeboy line three starts another loop nested

01:49

inside the first one and this time it's A four

01:52

loop Well four loops have three parameters The first being

01:55

the initialization imager J is one which is what we'll

01:58

be using is the eatery So write that on your

02:01

arm or whatever too The second is the termination parameter

02:07

When this condition is false the loop will no longer

02:10

run Yes j No longer being less than or equal

02:13

to I will stop the looting The third parameter is

02:19

called the increments and living up to its name It'll

02:23

increments j by one Each time the loop cycles Line

02:27

four is inside the loop It friends the product of

02:30

three times j and its base and he'll do it

02:34

over and over and over over within this loop until

02:38

j is no longer less than or equal to ay

02:42

well first time it runs Jay is one so we

02:45

print the product of three times one in a space

02:48

Then it'll increase j by one and a loop will

02:50

run again so next time it'll be three times too

02:53

and a space and then three times three and space

02:56

and three times for anna's face and three times five

02:59

in space And now jay six which is greater than

03:03

i look at your arms eyes five at the moment

03:06

That's the necessary condition for our four loop determining through

03:10

the chapel So now we move on to what happens

03:13

after the four loop which is an empty print line

03:16

statement that'll give us a new line and we subtract

03:19

one from i you all right But we're not done

03:24

The wild loop is still running And this time i

03:29

is for the interior Four loop is going to run

03:33

again and again until j is greater than i So

03:37

jay starts over at once and we'll print three times

03:40

one into space and three times do in the states

03:45

hand three times three spaces and three times for in

03:48

space but now has five which is greater than i

03:51

So we stopped the loop here and continue on with

03:53

an empty print line statement and decreasing i yet again

03:57

So from here we can totally tell what these loops

03:59

are doing and predict what will happen next The lupul

04:04

print three six nine and stop it because i will

04:07

be three And the local run again printing three six

04:18

and three At that point the wild loop will cease

04:24

running because i will no longer be greater than zero

04:28

Got all that and it looks like the result matches

04:31

up with the answer E and yeah that's our answer

04:34

and here's your smoke do sure brought to you by 00:04:37.173 --> [endTime] loops Wait not again Allright we're good out No

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