# AP Computer Science 3.1 Review of the Basics

AP Computer Science 3.1 Review of the Basics. What can you expect about the outcome from running this code?

 AP AP Computer Science AP Computer Science Review of the Basics Computer Science AP Computer Science Language English Language Program Analysis Debugging Test Prep AP Computer Science

### Transcript

00:19

shmoop overflowed running All right so let's go let's Start

00:25

with a look at what This coat actually does Step

00:27

by step we'll first we create a double variable called

00:30

numb with the value is your appoint one Then we

00:33

begin a four loop that starts with an injured eye

00:35

at zero stops when eyes no longer less than one

00:38

hundred and increment i by one Each time the loop

00:41

is run Essentially this loophole run one hundred times each

00:44

son loop cycles we make numb equal the value of

00:47

one divided by num minus nine point nine Phillips put

00:50

real numbers to it This means for the first generation

00:53

one divided by num a zero point one would equals

00:57

ten Got it one by one then ten minus nine

01:01

point nine his point one And we're back where we

01:03

started so Luke will run 99 more times and since

01:06

none will always equal point one when we cycle the

01:09

result will always be point one again In theory we're

01:13

dealing with a double variable here double means double precision

01:17

floating point variable got it and floating point variables aren't

01:22

the rigid representation of riel numbers we might expect In

01:26

fact the floating point bearable is more like a very

01:28

good guess at a very precise number It's never quite

01:32

exact even the very simple point one plus point two

01:35

in floating point variables wouldn't give you a point Three

01:38

you get something like point three zero zero for or

01:44

01:47

handy add the following lines to this code and run

01:51

it and we'll see what happens if you don't have

01:53

your compiler handy well and just we'll put system out

01:57

front line number right here in the loop That way

02:00

it'll print the current value of numb each time the

02:03

loop cycles and we'll be able to see how it

02:05

changes over time and for those not ableto participate Well

02:09

here's a picture of wild turkey these things you're huge

02:11

all right and here's what The result looks like weird

02:15

Right What happened Well the imperfections in the floating point

02:20

operations kept magnifying themselves over and over and over getting

02:24

worse and worse and loris with each iteration before finally

02:27

settling in at negative ten Those faras our potential answers

02:31

go option a Yep they're being overflowed No no overflow

02:35

ares occurred Option b there will be under flow so

02:39

after running numb will equal zero Also no option c

02:43

after running numb will equals your appointment Well sure the

02:46

code may look like things will remain in zero point

02:48

one on paper but using a floating point variable means

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the exact value of zero point one is not gonna

02:54

happen Option d after running none will not equal zero

02:58

point one Well that's right For a moment it even

03:01

seemed like num was equal to just about everything but

03:03

zero point one option e both andy well no ass

03:07

for overflow and there was no So our answer is

03:09

d and we're number one or rather we're number one 00:03:12.768 --> [endTime] point lobo too