Welcome to CS120Welcome to CS120

Fall 2012Fall 2012

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John MageeJohn Magee(jmagee@clarku.edu)(jmagee@clarku.edu)

Welcome to CS120Welcome to CS120

Computing is ubiquitousComputing is ubiquitous– Daily life, news, eCommerce…Daily life, news, eCommerce…– Sciences and engineering fieldsSciences and engineering fields– Social sciences, humanity,Social sciences, humanity,– Arts, music, sportsArts, music, sports– Education Education – ……

ComputingComputing One core objective of computing is efficient problem One core objective of computing is efficient problem

solving solving Computing shares common methodologies with Computing shares common methodologies with

other fieldsother fields

Given a problem, how toGiven a problem, how to– Understand it, formulate it, make hypotheses…Understand it, formulate it, make hypotheses…

Many computing problems come from other fieldsMany computing problems come from other fields

– Design a solutionDesign a solution strategies for big problems, such as divide and conquerstrategies for big problems, such as divide and conquer

– Implement a solutionImplement a solution Should be done in a systematic, disciplined fashionShould be done in a systematic, disciplined fashion

– Test a solutionTest a solution– Revise, improve…Revise, improve…

CS120CS120 Object-oriented programmingObject-oriented programming Graphics/animation-based problemsGraphics/animation-based problems Alice: A 3D animation languageAlice: A 3D animation language Java: an Eventful ApproachJava: an Eventful Approach Main topicsMain topics

– MethodsMethods– Variables and functionsVariables and functions– Control structuresControl structures– Lists and ArraysLists and Arrays– EventsEvents– ClassesClasses

Why Learn Programming?Why Learn Programming?

– Programming is a challenging and intellectually engaging experience.

– Programming is a part of computer science, and is therefore important to anyone interested in becoming a computer professional.

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Why Learn Programming?Why Learn Programming?

– Computers have become commonplace in our society, and understanding their strengths and limitations requires an understanding of programming.

– Programming can be a lot of fun.– Programming is a skill that can pay

the bills. Very well.

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About Learning to ProgramAbout Learning to Program

Pre-requisitesThis is a first course in computer science. There are no formal pre-requisites. Some informal pre-req’s:

– using email, browsing the web– copying and pasting text– some high-school level algebra

TimeAnyone can be successful at learning programming.Decent results, however, take a lot of time.

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How do we get there?How do we get there?

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LecturesTeaching LabsWeekly HomeworksProjectsMidtermWritten Exam and Practical Exam

ExpectationsExpectations

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AttendanceThis is not a correspondence course.

ParticipationQuestions and discussion are what makes the class interesting.

Administrative Questions?Administrative Questions?

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What You’ll Learn TodayWhat You’ll Learn Today

– What is computer science?What is computer science?– What is a computer?What is a computer?– What are hardware and software?What are hardware and software?– How can computers learn new tricks?How can computers learn new tricks?– What is Programming? What is Programming?

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What is Computer Science?What is Computer Science?

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What is CS?What is CS?

The fundamental ideas of CS are:The fundamental ideas of CS are:– AlgorithmsAlgorithms– ProtocolsProtocols– Encoding InformationEncoding Information– AbstractionAbstraction

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Flashlight MessagingFlashlight Messaging

Imagine you are 10 years old, in Imagine you are 10 years old, in 1980...1980...

Your best friend lives next door. Your best friend lives next door. You want to send messages at night.You want to send messages at night.

You each have a flashlight. You each have a flashlight. What do you do?What do you do?

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ABC means 123ABC means 123

13 5 5 20 13 5 5 20

13 5 13 5

1 20 1 20

19 20 1 18 2 21 3 11 1919 20 1 18 2 21 3 11 19

(Meet me at Starbucks)(Meet me at Starbucks)

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Numbered CodeNumbered CodeReplace each character with a number…Replace each character with a number…

Coded Message Example:Coded Message Example:13 5 5 20 13 5 1 20 19 20 1 18 2 21 3 11 1913 5 5 20 13 5 1 20 19 20 1 18 2 21 3 11 19

EncodingEncoding is about converting data into a coded is about converting data into a coded form.form.

DecodingDecoding is about converting from coded to normal is about converting from coded to normal form.form.

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AlgorithmAlgorithm

An An algorithmalgorithm is a is a sequence of clear and sequence of clear and precise step-by-step precise step-by-step instructions for solving instructions for solving a problem in a finite a problem in a finite amount of time.amount of time.

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ProtocolsProtocols

A A protocolprotocol is a set is a set of rules governing of rules governing the exchange or the exchange or transmission of transmission of data between data between devices.devices.

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The Braille Encoding The Braille Encoding SchemeScheme

Each character Each character is up to 6 dots. is up to 6 dots.

Each dot is Each dot is either on or off.either on or off.

Invented by Louis Braille (1809-1852).Invented by Louis Braille (1809-1852).

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What are we looking at?What are we looking at?

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No, No, thisthis is the matrix! is the matrix!

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What is this?What is this?

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Your web browser interprets Your web browser interprets the coded data (1s and 0s) the coded data (1s and 0s) and renders the Facebook and renders the Facebook webpage.webpage.

AbstractionAbstraction

AbstractionAbstraction is about hiding unnecessary is about hiding unnecessary details and retaining only the relevant details and retaining only the relevant information.information.

Eg. Eg.

““Tie your shoe”Tie your shoe”

““Drive a car”Drive a car”

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Encoding/DecodingEncoding/Decoding

The binary coded data (1s and 0s) is The binary coded data (1s and 0s) is what your web browser interprets as what your web browser interprets as the Facebook webpage. the Facebook webpage.

How?How?

The digital computer is a machine The digital computer is a machine which encodes, processes, and which encodes, processes, and decodes data.decodes data.

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Data and InformationData and Information

Data is a fact pattern:Data is a fact pattern:

Information is how we interpret that Information is how we interpret that pattern:pattern:

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What is a Computer?What is a Computer?

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What is a computer, anyway?

Give some examples:

A computer takes an input, applies a process, and produces an output.

What is a Computer?What is a Computer?

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HardwareHardware

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SoftwareSoftware

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Early History of ComputingEarly History of Computing

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Joseph Jacquard (1801) Jacquard’s Loom, the punched card

Harvard Mark IHarvard Mark I

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First Computer BugFirst Computer Bug

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Log of first computer bug, discovered by Grace Hopper, 1945A Computer Science Pioneer, she later wrote the first Compiler.

ProgrammabilityProgrammability

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What tricks does your computer do? – Web browsing, email, instant messenger– Play games– Watch movies, organize photos – Word processing, spreadsheets, database

Programmability is the ability to give a general-purpose computer instructions so that it can perform new tasks.

Programming LanguagesProgramming Languages

A program is a sequence of A program is a sequence of instructions.instructions.Spock: Spock: Computer. This is a Class-A compulsory directive. Computer. This is a Class-A compulsory directive. Compute, to the last digit, the value of pi.Compute, to the last digit, the value of pi.

Computers are not very good at Computers are not very good at understanding natural languagesunderstanding natural languages– Ambiguity and imprecisionAmbiguity and imprecision– Dialects, accents, etcDialects, accents, etc

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Programming LanguagesProgramming Languages

Computer languages are exact and Computer languages are exact and unambiguous.unambiguous.

Programming is the process of encoding our Programming is the process of encoding our ideas for the computer: ideas for the computer: – SyntaxSyntax (form) (form) – SemanticsSemantics (meaning) (meaning)

Popular programming languages:Popular programming languages:– BASIC, C++, Java, Perl, PythonBASIC, C++, Java, Perl, Python

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Machine LanguageMachine Language

Computing hardware performs only a small set of Computing hardware performs only a small set of concrete operations, which are created in circuitry:concrete operations, which are created in circuitry:

load the number from memory location 2001 into the CPUload the number from memory location 2001 into the CPUload the number from memory location 2002 into the CPUload the number from memory location 2002 into the CPUadd the two numbers in the CPUadd the two numbers in the CPUstore the result into location 2003store the result into location 2003

These instructions must be provided to the CPU as These instructions must be provided to the CPU as binary notation (1s and 0s), called machine binary notation (1s and 0s), called machine languagelanguage

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High Level LanguagesHigh Level Languages

Java is a high-level languageJava is a high-level language

c = a + bc = a + b

High level languages are more High level languages are more natural for us to understand, but natural for us to understand, but need to be translated into the need to be translated into the machine language for execution.machine language for execution.

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AliceAlice A modern programming toolA modern programming tool

– 3-D graphics3-D graphics– 3-D models of objects3-D models of objects

AnimationAnimation– Objects can be made to move around the Objects can be made to move around the

virtual world virtual world (a video game or simulation (a video game or simulation implemented in 3-D)implemented in 3-D)

Two kinds of animations:Two kinds of animations:– Movie: Movie: passive user watches the animationpassive user watches the animation

– Interactive: Interactive: active user clicks on mouse, types active user clicks on mouse, types a key on keyboard …a key on keyboard … Actions of user are called Actions of user are called eventsevents

Getting and Running AliceGetting and Running Alice Alice software is freely distributedAlice software is freely distributed Downloading AliceDownloading Alice

– Go to the website: Go to the website: http://www.alice.org – Click the link Get Alice 2.2Click the link Get Alice 2.2– Click download link specific to your operating Click download link specific to your operating

systemsystem– Save Save Alice.zipAlice.zip (or (or Alice.dmgAlice.dmg) to your PC) to your PC

Installing and running AliceInstalling and running Alice– Extract Alice from Extract Alice from Alice.zipAlice.zip (or (or Alice.dmgAlice.dmg) file) file– Create desktop shortcut (alias) to Alice.exeCreate desktop shortcut (alias) to Alice.exe– Double-click Alice icon to launch Alice applicationDouble-click Alice icon to launch Alice application

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Go through the Go through the tutorials to learn the tutorials to learn the basics of Alicebasics of Alice

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The Alice Tutorials (continued)

AliceAlice

Drag-and-drop based programmingDrag-and-drop based programming– Major advantage: preventing syntax errorsMajor advantage: preventing syntax errors– LimitationsLimitations

Restricted editingRestricted editing Restricted reusingRestricted reusing

– Statement resusable within a method (but not Statement resusable within a method (but not statements)statements)

– Clipboards available for copying and pasting statements Clipboards available for copying and pasting statements between methods of a class (but not all statements)between methods of a class (but not all statements)

– Saving a object (with newly defined methods) as a class Saving a object (with newly defined methods) as a class for using in other worlds for using in other worlds

Objects need to be pre-created (inconv. for Objects need to be pre-created (inconv. for arrays)arrays)

User StoriesUser Stories ContainContain

– Basic description of what happens when program runsBasic description of what happens when program runs– Nouns in story (Alice, the White Rabbit) correspond to Nouns in story (Alice, the White Rabbit) correspond to

objectsobjects– Verbs correspond to Verbs correspond to actions, responses to messagesactions, responses to messages– Chronological flow describes the sequence of the Chronological flow describes the sequence of the

actionsactions When the program begins, Alice and the White Rabbit are facing When the program begins, Alice and the White Rabbit are facing

each other, Alice on the left and the White Rabbit on the right. each other, Alice on the left and the White Rabbit on the right. Alice turns her head and then greets us. The White Rabbit also Alice turns her head and then greets us. The White Rabbit also turns and then greets us. Alice and the White Rabbit introduce turns and then greets us. Alice and the White Rabbit introduce themselves. Simultaneously, Alice and the White Rabbit say themselves. Simultaneously, Alice and the White Rabbit say “Welcome to our world.”“Welcome to our world.”

Alice in Action with JavaAlice in Action with Java 4444

User Story and Story BoardUser Story and Story BoardA numbered sequence of objects and actionsA numbered sequence of objects and actions1. Alice turns her head toward the user1. Alice turns her head toward the user

2. Alice greets the user2. Alice greets the user

3. The white rabbit turns toward the user3. The white rabbit turns toward the user

4. The white rabbit greets the user4. The white rabbit greets the user

5. Alice introduces herself5. Alice introduces herself

6. The white rabbit introduces himself6. The white rabbit introduces himself

7. Simultaneously, Alice and the white rabbit say7. Simultaneously, Alice and the white rabbit say

““Welcome to our world.”Welcome to our world.”

Alice in Action with JavaAlice in Action with Java 4545

Program DesignProgram Design For a given user story For a given user story

– plan scents and shotsplan scents and shots Scene: a piece of the story usually set in one Scene: a piece of the story usually set in one

locationlocation Shot: part of scene told with camera in one Shot: part of scene told with camera in one

positionposition

– Create storyboardsCreate storyboards

Alice in Action with JavaAlice in Action with Java 4646

Topics in CS120Topics in CS120

Eventful Java (tentative)Eventful Java (tentative)– EventsEvents– Primitive typesPrimitive types– Control StructuresControl Structures– Classes Classes – ArraysArrays– (Animation ?)(Animation ?)

What You Learned TodayWhat You Learned Today

– Computer Science is…Computer Science is…– A Computer is… A Computer is…

Hardware vs. SoftwareHardware vs. Software ProgrammabilityProgrammability

– Programming LanguagesProgramming Languages Machine language vs. high levelMachine language vs. high level

– Introducing Alice and JavaIntroducing Alice and Java

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Announcements and To Do Announcements and To Do ListList

– Visit the course web pageVisit the course web page– Download Alice 2.2Download Alice 2.2

Do the tutorialsDo the tutorials

– Readings:Readings: Alice in Action, Chapter 1Alice in Action, Chapter 1

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