Welcome to Computer Science III

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Welcome to Computer Science III

• The slides I will be using for this course are
  adapted from David Matuszek on-line course guide
  at http//www.cis.upenn.edu/matuszek

Ms. Van Nes Mercy High School
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Why are you here?

• There are two good reasons for getting into
  computer science
• The job market is (usually) very good
• Computer programming can be extremely satisfying
  and enjoyable
• To fulfill an elective requirement
• Which of these is more important?
• Money is a necessity
• Being rich isnt a necessity (but it sure is
  nice)
• You spend about 1/4 of your adult life working
• Its important to find work that you enjoy

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What are you getting yourself into?

• Programming is intellectually challenging
• It can be tremendous fun
• if you like that sort of thing!
• Lifelong learning is essential
• The technology is constantly changing
• We cannot teach you all you need to know
• We can point you in the right direction and give
  you a good, hard push--but the rest is up to you!

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Programming can be fun

• Programming is puzzle-solving
• Very little is mechanical, routine work
• You always have to be thinking
• If you like solving puzzles, theres a good
  chance you will like programming
• Some puzzles are hard
• You need a tolerance for frustration
• Solving hard puzzles can be very satisfying

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Computer Science

• Computer science is the study of
• what we can do with computers
• how we can best do it
• If we really understand how to do something, we
  can write a program to do it
• We do a lot of things without really
  understanding how we do them
• Computer science is all about how to do things

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CS III is a programming course

• Programming is teaching the computer how to do
  something
• Programming, like woodworking, is a craft
• To master a craft, you need both knowledge and
  experience
• Even a poor woodworker can produce a useable
  chair
• A master craftsman can produce a chair that is
  strong, comfortable, and beautiful

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Beauty in computer science

• Programs can be beautiful or ugly
• I am not speaking metaphorically
• Usually,
• Blind people cant appreciate fine paintings
• Deaf people cant appreciate good music
• Non-mathematicians cant appreciate elegant
  proofs
• Non-programmers cant appreciate the beauty in
  programs (but can often feel the lack of it!)

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Basic esthetics

• People have different tastes in music, but
• A two-year old pounding on a piano is not making
  music
• Very few musicians disagree on what notes make up
  a chord, or a chord progression
• People have different tastes in programming, but
  many values are held in common
• Programming is an art as well as a craft

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Elegance

• Powerful software can do everything you want to
  do--for example, Microsoft Word
• Complex software is hard to learn and hard to
  use--for example, Microsoft Word
• More power usually means more complexity
• Elegant software somehow manages to be both
  simple and powerful

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Elegance in mathematics

• In school, the mathematician Johann Carl
  Friedrich Gauss was told to add up the numbers
  from 1 to 100
• Gauss realized that 1 100 101,2 99 101,
  3 98 101, and so on
• There are fifty such pairs
• The answer must be 50 x 101, or 5050
• This is elegant it saves work, and its easy to
  understand

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Beauty in programming

• Outer beauty in programs consists of
• Doing a job the way the user wants it done
• Providing a simple, intuitive set of controls
• Working reliably, without crashes or glitches
• Inner beauty in programs consists of
• Simple, elegant, efficient solutions to problems
• Code that is easy to read, understand, and modify
• Good commenting and coding style

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Elegance in programming

• Consider the following problem
• You are given a stack of cards, allegedly
  containing the numbers 1 through 100...
• but there are only 99 cards
• How do you determine which card is missing?
• One solution
• Go through all the cards looking for 1, then do
  it again looking for 2, etc.
• Is there a better way?

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Elegance, again

• Suppose you are given a deck of 51 playing cards
• How do you decide which card is missing?
• Can you adapt Gausss solution to this problem?
• Suppose you are given one thousand decks, each
  missing one (not all the same) card
• For each deck, you want to find which card is
  missing
• Would the large number of decks change the way
  you solve the problem?

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What this class is about

• You need to learn the craft of programming
• How to design and write programs that work
• How to write clear code and documentation
• This is a skill, and it requires a lot of
  practice
• In this class we study programming
• You learn a language (Java 2) and some basic
  skills
• You learn how to use the language to tell the
  computer how to do things
• In this class we concentrate more on computer
  science
• Remember what I said If you really understand
  how to do something, you can write a program to
  do it
• Computer science is all about how to do things

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Out with the old, in with the new

• Geometry is about 2300 years old
• Its all based on straight lines and circles
• These were viewed as idealizations of nature
• There are no straight lines or circles in nature
• Didnt anybody notice?
• Benoit Mandelbrot developed fractal geometry
  starting in about 1977
• Even in a 2300 year old subject, things change!

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Changes in computer science

• Computer science is only about 55 years old
• Its changing much faster than geometry!
• Java is about seven years old
• We will be covering Java features that didnt
  exist this time last year
• Change is rapid and accelerating
• Dominant language of the 1990s C
• Dominant language of early 2000s Java
• Dominant company IBM to Microsoft to ?
• First GUI Macintosh, 1984
• First web browser Mosaic, 1992
• Web pages HTML to DHTML to XML

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Whats ahead?

• Half-life of CS knowledge about 5 years
• Typical length of career about 40 years
• What does this tell you?
• Nobody expected personal computers, graphical
  user interfaces, the mouse, the World Wide Web,
  the popularity of Java, the ascendance of XML,
  etc.
• There is only one safe prediction
• You will be taken by surprise!

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Maybe you should learn accounting instead?

• What can we possibly teach you that will do you
  any good five years from now?
• Many underlying programming concepts and
  mathematical foundations dont change
• Programming paradigms change slowly
• Each new language you learn will be easier to
  learn than the previous one, because most of the
  ideas in it will be familiar

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But more importantly...

• The attitude you need doesnt change
• Always be prepared to learn
• Take pride in your work, but--
• Realize that your work is not, and can never be,
  perfect
• Learn to welcome corrections and criticisms as
  helping you to perfect your work do not take
  them personally
• Seek out and fix problems, dont avoid them
• Be responsive to the realities of the situation

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A little problem
A
4
M
9

• I know each of the above cards has a letter on
  one side and a number on the other
• My theory is if a card has a vowel on one side,
  it has an even number on the other
• I want to test my theory, but...
• I want to turn over as few cards as possible
• Which cards must I turn over ?

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Answer to the cards problem

• Theory If vowel, then even

• You have to look for things that show you are
  wrong, not things that show you are right!
• This is part of what I mean by attitude

2
K
8
E
dontneed
need
dont need
need
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Small projects

• You can build a doghouse in a few hours
• You dont need a blueprint
• The materials dont cost much
• A little knowledge of tools is enough
• Imperfections are no big deal

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Medium-sized projects

• You can build a house in a year or so
• You really do need blueprints
• Excess materials mean wasted money

• House building requires more skills plumbing,
  bricklaying, electrical work, carpentry, etc.
• Imperfections matter you dont want a leaky
  roof!
• Its easier if you arent doing it all by yourself

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Large projects

• You cannot build a skyscraper by yourself
• Its just too much work for one person
• You dont have the money
• You dont have all the skills
• Imperfections could be costly or even fatal

• Skyscrapers can only be built by a team
• Communication is essential
• A paper trail is essential

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What does that mean for CS?

• What can we ask you to build in your classes?
• What will be expected of you in industry?
• We teach skyscraper-level skills, but
• we ask you to apply those skills to doghouses
• its silly, but what alternative do we have?
• Its up to you When you leave here,
• will you be able to build skyscrapers?
• or will you just be very good at building
  doghouses?

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Why am I here?

• My personal goals are
• For the students
• get everybody through this program
• with the skills and attitudes you need to succeed
• give you a solid understanding of basic
  programming
• try to lure you into learning more about the
  field
• For the program
• Produce really competent students that reflect
  well on Mercys Computer Science program

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Academia vs. industry

• In industry, the focus is on getting things done
• Your manager doesnt want duplication of
  efforttwo or more programmers doing the same
  thing
• If it helps get the job done, getting programs
  from somewhere elselegallyis fine
• Here, the emphasis is on learning how to do
  things
• We want duplication of effort
• We want you to all be learning the same things
• We want you to do all the work

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The Rules

• You may
• discuss the assignments with one another
• help others debug their work
• use, without attribution, anything I post to the
  Web
• You may not
• work together on the same program
• copy anothers code, or allow your code to be
  copied
• lend your code to someone else, or leave it lying
  around where someone else may copy it
• use any code from textbooks or the Web without my
  permission

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Group assignments

• The preceding rules apply to individual
  assignments
• This semester, some of the assignments will be
  done in pairsyou and another student working on
  the same problem
• The same rules apply, except that you and your
  partner will be treated as a single individual
• You and your partner will work on the same code,
  and together will turn in a single program
• You may not copy code from, or lend code to, any
  other pair
• We will discuss pair programming in substantially
  more detail later in the course

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How to get a good grade in here

• Start your assignments early!
• Programming takes a lot of time
• Its not easy to predict how long a program will
  take
• Test your programs thoroughly
• One or two simple tests are not enough
• We will do thorough testing, even if you dont!
• Read the assignments carefully
• Do what is assigned, not something like what is
  assigned
• Learn to use your tools
• Use comments and good style right from the
  beginning, not as a last-minute addition
• To prepare for tests, review and understand the
  lectures

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The End

• He who works with his hands is a laborer.
• He who works with his hands and his head is a
  craftsman.
• He who works with his hands and his head and his
  heart is an artist.
• -- St. Francis of Assisi