AP Computer Science Principles

For each online source, include the permanent URL. Identify the
author, title, source, the date you retrieved the source, and, if possible,
the date the reference was written or posted.
For each print source, include the author, title of excerpt/article and
magazine or book, page number(s), publisher, and date of publication.
If you include an interview source, include the name of the person you
interviewed, the date on which the interview occurred, and the
person’s position in the field.
Include citations for the sources you used, and number each source
accordingly.
Each source must be relevant, credible, and easily accessed.

Your resources must have identified relevant, credible, and easily
accessible sources to support your creation of the written responses to the
College Board prompts. You can search for print or nonprint sources as part
of your investigation. You can refer to a journal, a webpage, or an expert
that is being quoted as part of your written responses. Avoid plagiarism by
acknowledging, attributing, and/or citing sources throughout your
responses.

Generally, crowdsourced sites such as Wikipedia should be avoided.

The following will not receive ANY credit:

A. The response contains a list of sources only, no in-text citations;
B. The response contains less than three in-text citations; or
C. There are fewer than three sources cited, even if there are three or more

in-text citations.

Sample One:

1. Allen, Jaclyn. “Family Alleges GoFundMe Account Fraud after
$3,500 Meant to Pay for Funeral Disappeared.” The Denver Channel.
N.p., 15 June 2016. Web. 18 Oct. 2016.
<http://www.thedenverchannel.com/news/local-news/family-alleges-
gofundme-account-fraud-after-3500-meant-to-pay-for-funeral-
disappeared>.

2. Beaulieu, Halimah. “Turning Unmet Medical Needs into Big
Business: How Ethical Is Crowdfunding?” Simon Fraser University
News, 13 Oct. 2016. Web. 20 Oct. 2016.
<https://www.sfu.ca/sfunews/stories/2016/turning-unmet-medical-
needs-into-big-business.html>.

3. Brinkmann, Paul. “Pulse Fund on GoFundMe Nears $5M, Breaks
Records.” Orlando Sentinel. N.p., 16 June 2016. Web. 17 Oct. 2016.
<http://www.orlandosentinel.com/business/brinkmann-on-
business/os-fundraising-gofundme-record-20160616-story.html>.

4. Gestal, Laurie. “Lucky Pup Oliver’s Vet Bills.” GoFundMe.com.
N.p., 22 Oct. 2016. Web. 25 Oct. 2016.
<https://www.gofundme.com/luckypupoliver>.

5. GoFundMe. “About Us.” GoFundMe. N.p., n.d. Web. 17 Oct. 2016.
<https://www.gofundme.com/about-us>.

6. Primmer, Robert. “Robert Primmer.” Structured vs. Unstructured
Data. N.p., n.d. Web. 20 Oct. 2016.
<http://www.robertprimmer.com/blog/structured-vs-
unstructured.html>

Sample Two:

1. McKenzie, Kevin. “Memphis VA Promotes Suicide Prevention with
Comedy, Fashion.” The Commerical Appeal. USA Today, 7 Sept.
2016. Web. 9 Sept. 2016.

2. Rutkin, Aviva. “Extremists Are Turning Twitter and Facebook into
Theatres of War.” New Scientist, 7 Sept. 2016. Web. 9 Sept. 2016.

3. Heath, Sara. “How Social Media Can Improve Public Health, Patient
Education.” Patient Engagement HIT, 10 Oct. 2016. Web. 18 Oct.
2016.

4. “It’s What’s Happening.” Twitter, 30 June 2016. Web. 18 Oct. 2016.

Scoring Checklist

2a Computational Name of innovation
artifact Shows innovation running
States the purpose

2b Shows the function
2c Beneficial effect
and at least one Not graded but can reinforce 2a. State the steps
harmful effect used to not self-identify. Cite any music used.
2d Data
Beneficial effects on society, culture, or economy.
2e References Harmful effects on society, culture, or economy.

The data your innovation uses;
How the innovation consumes (as input), produces
(as output), and/or transforms data;
At least one data-storage concern, data-privacy
concern, or data-security concern directly related
to the computing innovation.

At least three online or print sources

2 Create Performance Task

It always takes longer than you expect, even when you take into account
Hofstadter’s Law.”

— Hofstadter’s Law

Chapter Goals

The Create Performance Task: 24% of grade
Programming
General requirements
Program requirements
Programming planning
Sample algorithms
Create sample program high scoring
Program checklist
Create sample program low scoring
Create sample program medium scoring
Submission requirements
Recording video
Compressing video
Sample 2a
Sample 2b
Sample 2c
Sample 2d

The Create Performance Task is worth 24 percent of your AP exam. If
careful attention is paid to the prompts and rubric, no points should be lost
on this section. The current prompts and rubric can be found on

apcentral.collegeboard.org. Make sure you are using the most current
version of the rubric as it can change.

Programming is a collaborative and creative process that brings ideas to
life through the development of software. Programs can help solve problems,
enable innovations, or express personal interests. In this performance task,
you will be developing a program of your choice. Your development process
should include iteratively designing, implementing, and testing your
program. You are strongly encouraged to work with another student in your
class for parts of this program.

WARNING: You are NOT allowed to work collaboratively on any part of
this performance task that is graded.

You are guaranteed at least 12 hours of class time and unlimited out of
class time to complete and submit the following:

A video of at least one significant feature of the program running

Written responses about your program and development process

Marked program code

GENERAL REQUIREMENTS

This performance task requires you to develop a program on a topic that
interests you or one that solves a problem. It is strongly recommended that a
portion of the program involve some form of collaboration with another
student in your class. Your program-development process must involve a
significant portion of work completed independently that requires a
significant level of planning, designing, and program development.

Parts of this task can be collaborative, but a significant part must be
completed independently.

The marked abstraction for grading is NOT a collaborative section.
The marked algorithms for grading is NOT a collaborative section.
The written portion is NOT a collaborative section.

PROGRAM REQUIREMENTS

Your program must demonstrate a variety of capabilities and implement
several different language features that, when combined, produce a result
that cannot easily be accomplished without computing tools and techniques.
Your program should draw upon a combination of mathematical and logical
concepts, such as use of numbers, variables, mathematical expressions with
arithmetic operators, logical and Boolean operators and expressions,
decision statements, iteration, and collections.

Your program can be written in ANY language. There is NO designed
programming language for AP Computer Science Principles. The difficulty
level of the program language is not considered in the scoring of this
performance task.

Your program must demonstrate:

Use of several effectively integrated mathematical and logical concepts
from the language you are using
Implementation of an algorithm that integrates other algorithms and
integrates mathematical and/or logical concepts
Development and use of abstractions to manage the complexity of your
program (e.g., procedures, abstractions provided by the programming
language, APIs)

The recommended completion date is prior to April 15th.
Your independently developed algorithms need to be fundamental for your
program to achieve its intended purpose.
There is NO designed programming language for AP Computer Science
Principles. Students may choose a programming language learned while
taking the course to complete the task, or they may select a different
programming language that they are familiar with outside of class.
Sample languages that can be used for the Create Performance Task:

JAVA Python SNAP Scratch
MobileCSP ALICE C++ Pascal
Machine Code LISP
COBOL C

Programming Planning

When selecting a programming language and the program focus, students
should ensure that their program will be sophisticated enough to integrate
mathematical and logical concepts, develop abstraction, and implement
algorithms.

A 500-line program will not necessarily score higher than a 30-line
program. In fact, a 500-line program that does not have abstractions (called
procedures, functions, or methods) and an algorithm that contains two
algorithms will score lower than the 30-line program if the 30-line program
contains all the correct elements.

The programming topic is completely up to you and should be something
that interests you. However, you need to account for the limited number of
classtime hours. If you want to write the new version of Halo, go for it.
However, Halo will not be able to be written in the provided 12 hours. Think
of the scope of your program before diving in. Still write the new version of
Halo, just do it on your non-AP time.

While writing the program you should be aware that your end program
requires an abstraction, two algorithms that combine to make one algorithm,
and the development process of two distinct points of difficulties or
opportunities when programming. At least one of these difficulties must
have been resolved independently.

Your algorithms do not have to be physically next to each other in the
code.

Examples of Starting Algorithms

Approximate counting algorithm
Correlation coefficient
Digital signature encryption algorithm
Card games
Dice games
Physics
Doomsday algorithm
Statistical algorithms
Easter algorithm
EIGamal asymmetric encryption algorithm
False position method in finding roots
Lesk algorithm

Parity error-detection technique
Pooled standard error
Projectile motion
Range
Standard deviation
Stemming algorithm
Total Energy = Kinetic Energy + Potential Energy
Variance
Zeller’s congruence

SAMPLE CODE
Example One

Sample One Statistics

Create an empty data structure and fill it with a large amount of
random numbers. Once the data structure is filled with random
numbers it opens up your program to contain statistics
algorithms.

Text-Based LOW SCORING

Score This program will score LOW because there is NO abstraction.
LOW The program also only contains the single algorithm num[x] =
rand.nextInt(100) + 1. Loops do not count as an algorithm.

Graphical-Based LOW SCORING

Score This program will score LOW because there is NO abstraction.
LOW The program also does not contain an algorithm. Loops do not
count as an algorithm.

Text-Based MEDIUM SCORING

Score This program will score MEDIUM because it does contain the

abstraction fillArray. The program contains a single algorithm

MEDIUM nums[x] = rand.nextInt(100) + 1. Loops do not count as an
algorithm.

Graphical-Based MEDIUM SCORING

Score This program will score MEDIUM because it does contain the

abstraction pickAnumber. The program does not contain an
MEDIUM algorithm. Loops do not count as an algorithm.

Text-Based HIGH SCORING



Score This program will score HIGH because contains an
HIGH abstraction. Actually, it contains the getMax, getMin, and
fillArray abstractions. The program also contains the algorithm
range, which uses two other abstractions, getMax and getMin.

Graphical-Based HIGH SCORING

The following program draws two line segments and then applies the line-
line intersection algorithm, which finds the point where two nonparallel lines
intersect.

Once the x and y intersection points are determined, the program then
determines if that point lies on one of the lines.













Score This program will score HIGH because it contains an
HIGH abstraction. Actually, it contains the doesIntersect,
getXIntersect, getYIntersect, MoveSprite, drawLine, and
getNum abstractions. The program also contains the algorithm
doesIntersect, which contains both a logical algorithm along
with a mathematical algorithm.

Checklist for High-Scoring Programming

Question Yes No

Does your program contain at least one
INDEPENDENTLY DEVELOPED abstraction?

Does your program contain one difficulty and/or
opportunity that you encountered and resolved?
Was development described as collaborative or
independent (at least one of the difficulties must be
resolved independently)?

Does your program contain another difficulty
and/or opportunity that you encountered and
resolved? Was the development described
collaborative or independent (at least one of the
difficulties must be resolved independently)?

Does your program contain two
INDEPENDENTLY DEVELOPED algorithms?

Does your program contain an INDEPENDENTLY
DEVELOPED algorithm that combines the two
algorithms?

Does at least one part of your program run?

Submission Requirements

Video

Submit one video in .mp4, .wmv, .avi, or .mov format that demonstrates the
running of at least one significant feature of your program. Your video must
not exceed one minute in length and must not exceed 30 MB in size.

There are many free screen-recording software options. PowerPoint Mix
can be used to record your program running using screen recording. To
record sound, a microphone is required. If your school blocks screen
recorders or you do not have access to microphones, consider recording your
program with a cell phone or external video recorder.

High-Scoring Video Yes No

High-Scoring Video Yes No

Show and narrate your program
compiling and running.

Describe the purpose of your
program.

Identify the computer language
used.

Do not self-identify.

Under 1 minute

If you record your program running using your phone, most likely your
video will exceed 30 MB. The College Board will not accept a video over 30
MB, so you will have to compress your video.

You can find an example video at https://youtu.be/w8bJgXgOIPA

Prompt 2a: Program Purpose and Development

Provide a written response or audio narration in your video that:
Identifies the programming language.
Identifies the purpose of your program.
Explains what the video illustrates.

(Approximately 150 words)

The programming language I used was Java and I used the Java IDE
environment Dr. Java.

The purpose of my program is to help people perform operations using
numbers. It is meant to be used as a tool that can quickly do what would
ordinarily be difficult for a person to do, like finding distance on a
coordinate plane, finding missing values in functions, finding missing sides
of triangles, and many more things. These types of functions are very useful
when doing different types of math.

The video illustrates all five components of this program running, showing
distance, triangle measurements, range, mass/density/volume, and

time/speed/distance methods running. My video illustrates running the range
for a 100-element array. It then shows the same range program running with
10 numbers in the data structure along with a 10,000 d=number data
structure.

2b

Describe the incremental and iterative development process of your
program, focusing on two distinct points in that process. Describe the
difficulties and/or opportunities you encountered and how they were
resolved or incorporated. In your description clearly indicate whether the
development described was collaborative or independent. At least one of
these points must refer to independent program development. (Must not
exceed 200 words)

Your two points can be two opportunities or two difficulties or one
opportunity and one difficulty. At least one of those points must have been
resolved independently. Use the term “I” when referring to the independent
process and “we” when referring to the collaborative process. The second
point described can be either independent or collaborative.

While the process may have been collaborative, ALL writing must be
done independently. When answering 2b take the reader through the entire
development process. Don’t just state the difficulty or opportunity.

I needed to fill up an array with randomly generated numbers. I created
an abstraction called fillArray to compartmentalize the code and a while
loop to access each element of the data structure. My difficulty is I tried to
use the Random() method but it was giving me an error. I resolved this error
by independently researching on Google “how to generate a random number
in java.” I discovered the website stackoverflow. It instructed me to import
java.util.Random, then create a random object and use the method
nextInt(50)+ 1. I implemented the code and it worked! I did have to change
the 50 to a 100 because I wanted 100 random numbers, not 50.

I also had a difficulty in creating abstractions. I wanted to create an
abstraction to return the maximum number in the array. When I compiled the
program I got the following error.

2 errors found:
File: C:\Users\seth_\Documents\MySample.java [line: 17]
Error: nums cannot be resolved to a variable
File: C:\Users\seth_\Documents\MySample.java [line: 19]
Error: nums cannot be resolved to a variable
From the error I determined that the data structure I called nums scope is
not covered by the abstraction. To fix this I looked at old code on
codingbat.com and determined that I should pass nums as a formal
parameter. My excitement was short lived as I got the following error.
1 error found:
File: C:\Users\seth_\Documents\MySample.java [line: 12]
Error: Cannot make a static reference to the non-static method
getMax(int[]) from the type MySample
By looking at the error and noticing the words non-static method I
changed my method header to include static as the second word of the
method header. Success! The method now works as intended.

2c

Capture and paste a program code segment that implements an algorithm
(marked with an oval in section 3 below) and that is fundamental for your
program to achieve its intended purpose. This code segment must be an

algorithm you developed individually on your own, must include two or
more algorithms, and must integrate mathematical and/or logical concepts.
Describe how each algorithm within your selected algorithm functions
independently, as well as in combination with others, to form a new
algorithm that helps to achieve the intended purpose of the program. (Must
not exceed 200 words)

This algorithm’s purpose is to find the range in a set of numbers
previously inputted by the user. The method findRange() is called if the user
selects the option 3. This algorithm first calls findMax(), which returns the
maximum value in the set of numbers the user previously inputted. Next it
calls findMin(), which returns the minimum value in the set. Individually,
findMax() finds the largest number in the set by setting max equal to the first
value then checking each following value, replacing max if the number is
larger. Individually findMin() finds the smallest number in the set by setting
min equal to the first value and checking every other value, replacing min if
the number is smaller. Together, these two algorithims are used to make
findRange() work by doing findMax() minus findMin() and prints the range
value. This accomplishes the task of this algorithmic method to find range,
an integral part of the entire function of the program to help with number
functions.

Written Response 2d

Capture and paste a program code segment that contains an abstraction you
developed individually on your own (marked with a rectangle in section 3).
This abstraction must integrate mathematical and logical concepts. Explain
how your abstraction helped manage the complexity of your program. (Must
not exceed 200 words)

The purpose of the abstraction findDistanceBetweenTheTwoPoints() is to
take the two points that were inputted by the user in a previous abstraction
and find the distance between them on the coordinate plane. This abstraction
is called if the user selects option 1 when given their choices, which finds
coordinate plane distance. After the method to collect the points has run,
findDistanceBetweenTheTwoPoints() is called. Within this abstraction the
formula for distance is used. However, to further manage the complexity, two
more abstractions are called, both of which return integer values back to
findDistanceBetweenTheTwoPoints(). The first method, xValuesSquared(),
takes the first and second x values, subtracts them, then squares the
difference. The second method, yValuesSquared(), is identical but uses y
values. These values are returned to findDistanceBetweenTheTwoPoints(),
where they are used as needed in the formula—added and then square
rooted. This manages complexity because it allows anyone reading the
program to see much more clearly what is going on.
findDistanceBetweenTheTwoPoints() also manages complexity since it lets
me more easily change my program if I wanted to move which option
number I wanted distance to be. Were the method
findDistanceBetweenTheTwoPoints() not in the program it would not
properly function when the user chose option 1 to find distance as it serves
to use the user’s input to output the distance that they are looking for.

3 Abstraction

BIG IDEA 2: ABSTRACTION

“We are so much the victims of abstraction that with the Earth in flames we
can barely rouse ourselves to wander across the room and look at the
thermostat.”

—Terence McKenna

Chapter Goals

What is an abstraction?
Machine code
Binary sequences
Software abstractions
Converting numbers to decimal
Overflow errors
Models and simulations
Programming levels
Hardware abstractions
Abstraction examples
Converting numbers from decimal
Roundoff errors
Abstraction questions

What Is an Abstraction?

In computer science, an abstraction is a way to represent essential features
without including the background details or explanations. Abstractions

reduce complexity and allow efficient design and implementation of
complex software systems. Abstraction become a necessity as systems
become more complex. For example, any time you check your stories on
Instagram you are using a bunch of processes in the background that you
have no control over. Without these abstractions it would be difficult to send
a message to a friend. With the use of abstractions you can focus on content,
not the technical details of how the application works.

Programmers also use abstractions. Rarely will programmers deal directly
in machine code. Machine code is a base language where no abstractions are
implemented. Programmers have worked to hide details by using
abstractions. This allows the user to focus on the problem. Think of it as
comparable to a problem of driving. A user’s job is to navigate a course at
speed. Abstraction keeps the details “under the hood” so that the “driver can
drive.” The driver has his/her job and does not need to worry about what
makes the engine run; abstraction allows the machine to run and the driver
or user to navigate his or her challenge.

Programming Language Levels

Abstractions find common features to generalize the program. This can also
help shrink the code if you are planning to use a method/procedure more
than once in a program. Instead of repeating the code lines you can
reference a prior set of directions—to repeat the outcome without having to
rewrite the lines of code. By reducing the number of lines of code, chances
for errors are also reduced.

For example:
Adding the number 1234 + 4321 in an upper-level language with
abstractions could look something like this for the language of JAVA: int
x = 1234 + 4321. In Python it would look something like x = 1234 +
4321. Without abstractions and using just machine code the same math
example would look like 10111001 11010010 0000011 100001001
00001110 00000000 00000000 10111001 11100001 00010000 10001001
00001110 00000010 00000000 10100001 00000000 00000000 1001011
00011110 00000010 00000000 00000011 11000011 10100011 00000100
00000000.
High-level languages contain the most abstractions and allow for easier
coding and easier debugging.

Hardware Abstractions

At the lowest level, computers are built on transistors. Transistors are tiny
switches that have two settings: on and off. A binary off is represented by 0,
and a binary on is represented by 1.

The current size of a transistor is approximately 10 nm long. More than
30,000 million transistors can fit on a single computer chip. The details of
how semiconductors work is beyond the scope of this class.

To program a computer, we would have to feed it all 0’s and 1’s if not for
abstractions. These low-level languages are extremely difficult to program
and debug. To make programming easier, multiple layers of abstractions are
used. Abstractions hide details, allowing the programmer to focus on
solving problems.

At the lowest level, all digital data are represented by bits. For example,
the letter a is an abstraction for 01000001. At a higher level, bits are
grouped to represent abstractions, including but not limited to numbers,
colors, characters, audio, and pictures.

BINARY SEQUENCES

A variety of abstractions built on binary sequences can be used to represent
all digital data. Binary sequences can represent color, Boolean logic, lists,
and so on. Anything that can be stored on a computer can be represented by
binary sequences.

A pixel of light red can also be represented as binary numbers at the
lowest level. For example, the maximum red value of a pixel is an
abstraction for the binary number 1111 1111 0011 0011 0110 0110.

Abstraction Examples

The process of developing an abstraction involves removing detail and
generalizing functionality. Different program languages offer different
levels of abstractions. High-level programming languages provide more
abstractions than lower-level languages. Coding in a programming language
is often translated into code in another low-level language that the computer
can execute.

Text: Displays the value of
DISPLAY (expression) expression, followed by a
space.
Block:

DISPLAY(expression) is an abstraction that is used on your AP test to
display a value of expression followed by a space. The input parameter for
the DISPLAY abstraction is expression.

Text: Evaluates to a random integer from
RANDOM (a, b) a to b, including a and b.

Block: For example, RANDOM (1,3)
could evaluate to 1, 2, or 3.

RANDOM

Another abstraction used on your AP test is RANDOM(a, b), which
evaluates to a random number from a to b inclusive. The input parameters in
this abstraction are a and b.

Both abstractions were coded one time but can be used an unlimited
amount of times without rewriting the code. This code reuse saves time and
can prevent errors when writing code.

An abstraction generalizes functionality with input parameters that allow
software reuse. Being aware of and using multiple levels of abstractions in
developing programs helps to more effectively apply available resources
and tools to solve problems.

A way to handle complex tasks and ideas is to “chunk” them into smaller,
more manageable concepts/sections. This allows us to address each term
itself, rather than all the supporting components.

Software Abstraction Levels

Hardware Abstraction Levels

Hardware also has levels of abstractions.

Converting Numbers

Number bases, including binary, decimal, and hexadecimal, are used to
represent and investigate digital data.

Part of the AP test is converting numbers from any base to any other
base. We will focus on the more popular conversions where the rules can
apply to any conversion.

Decimal Hexadecimal Binary
0 0 0000
1 1 0001
2 2 0010
3 3 0011

Decimal Hexadecimal Binary
4 4 0100
5 5 0101
6 6 0110
7 7 0111
8 8 1000
9 9 1001
10 A 1010
11 B 1011
12 C 1100
13 D 1101
14 E 1110
15 F 1111

Example One

Converting Binary (BIN) Numbers to Decimal (DEC)
11011BIN = ?DEC
Step 1. A five-column table is needed because 11011 has five numbers. Start
by putting a 1 in the upper-right box of the five-column table.

1

Step 2. Fill in the remaining first row by continually multiplying by the
base. Because the base number is in binary, fill the columns by continually
multiplying the product by 2.

8 × 2 = 16 4 × 2 = 8 2×2=4 1×2=2 1

Step 3. Place the numbers to be converted in the second row. 1
1
16 8 4 2
1101

Step 4. Add the result of multiplying row one with row two.
16 × 1 + 8 × 1 + 4 × 0 + 2 × 1 + 1 × 1 = 27DEC

Example Two

110BIN = ?DEC

Use a three-column table and multiply the top row by the base number
starting with 1 in the upper-right box.

421
110

Add the result of multiplying row one with row two.

4 × 1 + 2 × 1 + 1 × 0 = 6DEC

Example Three

11011011BIN = ?DEC

Use an eight-column table and multiply the top row by the base number
starting with 1 in the upper-right box.

128 64 32 16 8 4 2 1

11011011

Add the result of multiplying row one with row two.

128 × 1 + 64 × 1 + 32 × 0 + 16 × 1 + 8 × 1 + 4 × 0 + 2 × 1 + 1 × 1 = 219DEC
Hexadecimal (base 16)

Example Four

Converting Hexadecimal (HEX) Numbers to Decimal (DEC)
12HEX = ?DEC
Step 1. A two-column table is needed because 12 has two numbers. Start by
putting a 1 in the upper-right box of the two-column table.

1

Step 2. Fill in the remaining first row by continually multiplying by the
base. The base number is in HEX, so fill the columns by continually
multiplying the product by 16.

1 × 16 = 16 1

Step 3. Place the numbers to be converted in the second row.

16 1
12

Step 4. Add the result of multiplying row one with row two.

16 × 1 + 1 × 2 = 18DEC

Decimal (base 10) goes from 0 to 9, which contains 10 numbers.
Binary (base 2) goes from 0 to 1, which contains two numbers.
Hexadecimal (base 16) goes from 0 to 15, which contains 16 numbers. To
represent the numbers 10 through 15 the letters A to F are used.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
ABCDE F

Example Five

2BHEX = ?DEC
Use a two-column table and multiply the top row by the base number
starting with 1 in the upper-right box.

16 1
2 11

Add the result of multiplying row one with row two.
16 × 2 + 1 × 11 = 43DEC

Example Six

AD HEX = ?DEC
Use a two-column table and multiply the top row by the base number
starting with 1 in the upper-right box.

16 1
10 13

Add the result of multiplying row one with row two.
16 × 10 + 1 × 11 = 171DEC

Example Seven

Octal (base 8)
Converting Octal (OCT) Numbers to Decimal (DEC)

28OCT = ?DEC

Step 1. A two-column table is needed because 28 has two numbers. Start by
putting a 1 in the upper-right box of the two-column table.

1

Step 2. Fill in the remaining first row by continually multiplying by the
base. Since the base number is in octal, fill the columns by continually
multiplying the product by 8.

1×8=8 1

Step 3. Place the numbers to be converted in the second row.

81
28

Step 4. Add the result of multiplying row one with row two.
8 × 2 + 1 × 8 = 24DEC

Example Eight

127OCT = ?DEC
Use a three-column table and multiply the top row by the base number
starting with 1 in the upper-right box.

64 8 1
12 7

Add the result of multiplying row one with row two.

64 × 1 + 8 × 2 + 1 × 7 = 87DEC

Example Nine

Converting Numbers from Decimal
46DEC = ?BIN

Step 1. Create a flexible table with enough columns until the number in the
upper row is just bigger than the number you are converting to.

(64 is bigger than 46)

64 32 16 8 4 2 1

Step 2. Start with the largest number that is still smaller than the target
number.

64 32 16 8 4 2 1

1

Subtract the table number from the base number.
46 - 32 = 14DEC
Can 16 fit into 14? No, it cannot.

64 32 16 8 4 2 1

10

14 - 0 = 14
Can 8 fit into 14? Yes, it can.

14 - 8 = 6

64 32 16 8 4 2 1

101

Can 4 fit into 6? Yes, it can.
6-4=2

64 32 16 8 4 2 1

1011

Can 2 fit into 2? Yes, it can.
2-2=0

64 32 16 8 4 2 1

10111

Can 1 fit into 0? No.

64 32 16 8 4 2 1

101110

Answer: 101110BIN.

Example Ten

30DEC = ?BIN

Step 1. Create a flexible table with enough columns until the number in the
upper row is just bigger than the number you are converting to.

32 16 8 4 2 1

Step 2. Start with the largest number that is still smaller than the target
number.
30 - 16 = 14

32 16 8 4 2 1
1

14 - 8 = 6

32 16 8 4 2 1
11

6-4=2

32 16 8 4 2 1
111

2-2=0

32 16 8 4 2 1
1111

0

32 16 8 4 2 1
11110

Answer: 11110BIN.

Example Eleven

130DEC = ?HEX

Step 1. Create a flexible table with enough columns until the number in the
upper row is just bigger than the number you are converting to.

256 16 1

120 - (16 × 8) = 2 16 1
256 8
1
2 - (1 × 2) = 0 16 2
256 8

Answer: 82HEX.

Example Twelve

163DEC = ?HEX

Step 1. Create a flexible table with enough columns until the number in the
upper row is just bigger than the number you are converting to.

256 16 1

163 - (16 × 10) = 3 16 1
256 A

3 - (1 × 3) = 0

256 16 1
A 3

Answer: A3HEX.

Binary numbers can be conveniently represented by hexadecimal numbers,
where one hexadecimal number represents four binary numbers.

Example Thirteen D
13
Converting Hexadecimal to Binary
Convert BDHEX to BIN 8421
1101
B
11

8421
1011

Answer: BDHEX = 10111101BIN.

Example Fourteen 9

Convert A9HEX to BIN 8421
10 1001

8421
1010

Answer: A9HEX = 10101001BIN.

Example Fifteen

Convert EEHEX to BIN 15
15
8421
8421 1111
1111
Answer: EEHEX = 11111111BIN.

Overflow Errors

In many programming languages a fixed number of bits is used to represent
characters or integer limits. For example, in JAVA integers have a range
from -2,147,483,648 to 2,147,483,647. These limits can result in overflow
or other errors.

Example One 1

What is the largest value stored using two bits?

2

The largest number would be 11BIN.

21
11

2×1+1×1=3
The smallest number would be 0.
Two bits can store numbers from 0 to 3, which is 4 numbers, or 22.
If you try to store the number 4 or greater in a two-bit system, you will get
an overflow error.

Example Two

Using a two-bit system, what would result in add 5 + 3?
Answer: To store the number 8 would require a four-bit system, so this is an
overflow error.

Example Three

What is the largest value stored using three bits?

421
111

Largest number: 4 × 1 + 2 × 1 + 1 × 1 = 7
Smallest number: 0
Two bits can store numbers from 0 to 7, which is 8 numbers, or 23.
If you try to store the number 9 or greater in a three-bit system, you will get
an overflow error.

Example Four

What is the largest value stored using four bits?

8421
1111

Largest number: 8 × 1 + 4 × 1 + 2 × 1 + 1 × 1 = 15
Smallest number: 0
Two bits can store numbers from 0 to 15, which is 16 numbers, or 24.

Example Five

What is the largest value stored using eight bits?
The largest number is 255: 28 = 256 numbers from 0 to 255.
For every additional bit the amount of numbers stored is squared.

Roundoff Errors

A roundoff error occurs when decimals are rounded. One computer might

calculate = .333333. Another computer might calculate =

.3333333333. In this case on one computer is not equal to on a

second computer.
At a higher level, bits are grouped to represent abstractions, including

(but not limited to) numbers, colors, characters, audio, and pictures.
Computer hard drives contain many bits of storage. For example, a
computer with eight gigabytes of memory has 8,589,934,592 bits.

MODELS AND SIMULATIONS

Models and simulations use abstractions to generate new understanding and
knowledge.

Models and simulations are tools frequently used to represent objects or
phenomena that could not easily be replicated on a similar scale.
Simulations are often used to test safety features or changes in business
models without affecting customers while testing. The benefit of using a
computer program to test a car crash, for example, rather than physically
crashing a car is clear—it is less expensive and significantly less dangerous.
The real crash, however, is affected by more variables than can be coded
into a simulation and is more accurate as a result. Simulations require more
abstractions as they become more complex; a simulation of a car crash will
require more abstractions than one of a simpler task, such as dropping a ball
from a given height.

The use of models and simulations allows for the user to gain insight on
the workings of a particular object or phenomenon. The outcomes of each
simulation or model accumulate to allow the formation of a hypothesis, or a
proposed explanation of a phenomenon that serves as a starting point for
further simulations. Testing a hypothesis through simulations is speedier and
more easily done in comparison to testing a hypothesis through the real
world. It allows testing in conditions that may not be possible on Earth, like

that of a vacuum. The more detail put into testing a hypothesis, the more
time and equipment required to run the program.

Generally, the more variables considered in a simulation, the more
accurate the simulation is.

ABSTRACTION QUESTIONS

DIRECTIONS: Each of the questions or incomplete statements
below is followed by four suggested answers or completions. Select
the one that is best in each case.

1. Convert 100001BIN to a decimal number.
A. 29
B. 33
C. 31
D. 63

2. Convert 111111BIN to a decimal number.
A. 29
B. 33
C. 31
D. 63

3. Convert 2DHEX to a decimal number.
A. 29
B. 33
C. 31
D. 45

4. Convert 1FHEX to a decimal number.
A. 29
B. 33

C. 31
D. 45

5. Convert 1101BIN to a decimal number.

A. 11
B. 1
C. 13
D. 1101

6. Convert 48HEX to a decimal number.

A. 44
B. 54
C. 72
D. 89

7. Convert 8HEX to a decimal number.

A. 44
B. 54
C. 72
D. 8

8. Convert ADHEX to a decimal number.

A. 44
B. 54
C. 87
D. 173

9. Convert 48OCT to a decimal number.

A. 40
B. 55
C. 80
D. 89

10. Convert AAHEX to a decimal number.