8/27/2012

1

Welcome to CS120

Fall 2012

1

John Magee (jmagee@clarku.edu)

Welcome to CS120

Computing is ubiquitous

– Daily life, news, eCommerce…

– Sciences and engineering fields

– Social sciences, humanity,

– Arts, music, sports

– Education

– …

8/27/2012

2

Computing One core objective of computing is efficient problem solving

Computing shares common methodologies with other fields

Given a problem, how to

– Understand it, formulate it, make hypotheses…

Many computing problems come from other fields

– Design a solution

strategies for big problems, such as divide and conquer

– Implement a solution

Should be done in a systematic, disciplined fashion

– Test a solution

– Revise, improve…

CS120 Object-oriented programming

Graphics/animation-based problems

Alice: A 3D animation language

Java: an Eventful Approach

Main topics

– Methods

– Variables and functions

– Control structures

– Lists and Arrays

– Events

– Classes

8/27/2012

3

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.

5

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.

6

8/27/2012

4

About Learning to Program

Pre-requisites

This 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

Time Anyone can be successful at learning programming.

Decent results, however, take a lot of time.

7

How do we get there?

8 9

Lectures

Teaching Labs

Weekly Homeworks

Projects

Midterm

Written Exam and Practical Exam

8/27/2012

5

Expectations

9 9

Attendance This is not a correspondence course.

Participation Questions and discussion are what makes the class

interesting.

Administrative Questions?

10 9

8/27/2012

6

What You’ll Learn Today

– What is computer science?

– What is a computer?

– What are hardware and software?

– How can computers learn new tricks?

– What is Programming?

11

What is Computer Science?

12

8/27/2012

7

What is CS?

The fundamental ideas of CS are:

– Algorithms

– Protocols

– Encoding Information

– Abstraction

13

Flashlight Messaging

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

Your best friend lives next door.

You want to send messages at night.

You each have a flashlight.

What do you do?

14

8/27/2012

8

ABC means 123

13 5 5 20

13 5

1 20

19 20 1 18 2 21 3 11 19

(Meet me at Starbucks)

15

Numbered Code

Replace each character with a number…

Coded Message Example:

13 5 5 20 13 5 1 20 19 20 1 18 2 21 3 11 19

Encoding is about converting data into a coded form.

Decoding is about converting from coded to normal form.

16

8/27/2012

9

Algorithm

An algorithm is a

sequence of clear and

precise step-by-step

instructions for solving

a problem in a finite

amount of time.

17

Protocols

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

18

8/27/2012

10

The Braille Encoding Scheme

Each character is up to 6 dots. Each dot is either on or off.

Invented by Louis Braille (1809-1852).

19

What are we looking at?

20

8/27/2012

11

No, this is the matrix!

21

What is this?

22

8/27/2012

12

23

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

Abstraction

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

Eg.

“Tie your shoe”

“Drive a car”

24

8/27/2012

13

Encoding/Decoding

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

How?

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

25

Data and Information

Data is a fact pattern:

Information is how we interpret that pattern:

26

8/27/2012

14

What is a Computer?

27 2

What is a computer, anyway?

Give some examples:

A computer takes an input, applies a

process, and produces an output.

What is a Computer?

28

8/27/2012

15

Hardware

29 3

Software

30 3

8/27/2012

16

Early History of Computing

31

Joseph Jacquard (1801)

Jacquard’s Loom, the punched card

Harvard Mark I

32 IBM Archives

8/27/2012

17

First Computer Bug

33

Log of first computer bug, discovered by Grace Hopper, 1945

A Computer Science Pioneer, she later wrote the first Compiler.

Programmability

34 3

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.

8/27/2012

18

Programming Languages

A program is a sequence of instructions.

Spock:

Computer. This is a Class-A compulsory directive. Compute, to the last digit, the value of pi.

Computers are not very good at understanding natural languages – Ambiguity and imprecision

– Dialects, accents, etc

35

Programming Languages

Computer languages are exact and unambiguous.

Programming is the process of encoding our ideas for the computer:

– Syntax (form)

– Semantics (meaning)

Popular programming languages:

– BASIC, C++, Java, Perl, Python

36

8/27/2012

19

Machine Language

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

load the number from memory location 2001 into the CPU

load the number from memory location 2002 into the CPU

add the two numbers in the CPU

store the result into location 2003

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

37

High Level Languages

Java is a high-level language

c = a + b

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

38

8/27/2012

20

Alice A modern programming tool

– 3-D graphics

– 3-D models of objects

Animation – Objects can be made to move around the

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

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

– Interactive: active user clicks on mouse, types a key on keyboard …

Actions of user are called events

Getting and Running Alice

Alice software is freely distributed

Downloading Alice – Go to the website: http://www.alice.org

– Click the link Get Alice 2.2

– Click download link specific to your operating system

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

Installing and running Alice – Extract Alice from Alice.zip (or Alice.dmg) file

– Create desktop shortcut (alias) to Alice.exe

– Double-click Alice icon to launch Alice application

41

8/27/2012

21

Go through the

tutorials to learn

the basics of Alice

42

The Alice Tutorials (continued)

Alice

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

– Limitations Restricted editing

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

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

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

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

8/27/2012

22

User Stories Contain

– Basic description of what happens when program runs

– Nouns in story (Alice, the White Rabbit) correspond to objects

– Verbs correspond to actions, responses to messages

– Chronological flow describes the sequence of the actions

When the program begins, Alice and the White Rabbit are facing 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 turns and then greets us. Alice and the White Rabbit introduce themselves. Simultaneously, Alice and the White Rabbit say “Welcome to our world.”

Alice in Action with Java 44

User Story and Story Board A numbered sequence of objects and actions

1. Alice turns her head toward the user

2. Alice greets the user

3. The white rabbit turns toward the user

4. The white rabbit greets the user

5. Alice introduces herself

6. The white rabbit introduces himself

7. Simultaneously, Alice and the white rabbit say

“Welcome to our world.”

Alice in Action with Java 45

8/27/2012

23

Program Design

For a given user story

– plan scents and shots

Scene: a piece of the story usually set in one location

Shot: part of scene told with camera in one position

– Create storyboards

Alice in Action with Java 46

Topics in CS120

Eventful Java (tentative)

– Events

– Primitive types

– Control Structures

– Classes

– Arrays

– (Animation ?)

8/27/2012

24

What You Learned Today

– Computer Science is…

– A Computer is…

Hardware vs. Software

Programmability

– Programming Languages

Machine language vs. high level

– Introducing Alice and Java

48

Announcements and To Do List

– Visit the course web page

– Download Alice 2.2 Do the tutorials

– Readings:

Alice in Action, Chapter 1

49