Welcome to CS 100

1
Welcome to CS 100

• Goal Learn to write intelligible, correct
  computer programs
• Language Java (but the language should not be
  the primary focus)
• Software CodeWarrior
• Plan Compressed, intense version of a
  full-semester course. Be sure to keep up!

2
Course Staff

• Instructor Lynette Millett, millett_at_cs
• TAs
• Wei Tsang Ooi, weitsang_at_cs.cornell.edu
• Alan Renaud, ajr5_at_cornell.edu
• David Welte, dcw6_at_cornell.edu
• Consultants
• Rocky Chen, pjc4_at_cornell.edu, Young Ho Cho,
  yc102_at_cornell.edu, Amanda Waack, amw18_at_cornell.edu

3
Logistics

• Lectures every day (Mon-Fri)
• Roughly two assignments per week
• NO LATE ASSIGNMENTS ACCEPTED
• 0 or more short quizzes per week
• Partners 1 partner allowed where specified
• Highest level of academic integrity expected

4
Logistics continued

• Office hours as noted on web
• One prelim Monday, July 19, 1999
• Final Grades
• 50 assignments
• 25 prelim
• 25 final
• First Assignment due this THURSDAY

5
When Turning in Assignments

• No late assignments accepted
• Your name and Cornell ID should be on frontpage
  (in comments, if a program)
• For programming assignments turn in printout of
  source code, sample output and disk
• For written assignments please type. TAs reserve
  right not to grade illegible homework.

6
Main Concepts Today

• What is an algorithm?
• Method and method call
• Reading this week Chapter 1 (skim), Chapters 2
  and 3
• Handouts

7
Algorithm

• A set of instructions for performing some task
  that is
• precise
• unambiguous
• effective
• abstract
• In other words well-specified

8
Examples of Algorithms

• A recipe for chocolate mousse
• Given this list of integers, tell me which ones
  are even
• Play a game of tic-tac-toe in a way that you
  never lose
• Find your Star Wars name

9
Star Wars example

• First SW name Write first 3 letters of your last
  name then attach first 2 letters of your first
  name
• Last SW name Write first 2 letters of mothers
  maiden name and attact first 3 letters of hometown

Lynette Millett born in Norway, ME to I. (Rogers)
Millett becomes MilLy Milly RoNor Ronor
10
Ambiguous Algorithm

• Take two pieces of bread
• Put peanut butter on one side of one piece
• Put jelly on one side of the other piece
• Put the pieces together
• Output of this algorithm is. . . .

11
A Messy Sandwich

• Why?
• The algorithm did not specify that the pieces of
  bread should be put together so that the peanut
  butter and jelly are on the inside
• Computers do exactly what theyre told or, worse,
  something undefined
• Precision is important
• Any other ambiguities in that example?

12
Programs

• A program is an algorithm written in some
  language English, C, Java, . .
• Computer program is a program in a computer
  language such as Java
• Abstraction vs. Representation
• Algorithm -- Program
• Number -- Numeral
• Object having threeness -- 3, III, three,

13
How does it work?

• Algorithm given as sequence of instructions to
  execute in order
• In Java, each instruction is called a statement
• Common statement in Java is a method call or
  method invocation
• But, whats a method?
• Method, procedure, function often used
  interchangeably

14
Sample Method Heading
// Draw a line from point (x1, y1) to point
//(x2, y2) public void drawLine (int x1, int
y1, int x2, int y2)

• Comment explains the method precisely in
  English. Always begin with //
• Prefix modifiers public, void (will explain
  later)
• Method name drawLine
• Parameters x1, y1, x2, y2, and their types int

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Method Call
// Draw a line from point (x1, y1) to point
//(x2, y2) public void drawLine (int x1, int
y1, int x2, int y2)

• Call drawLine(3, 5, 1, 1)
• Command to be executed Draw a line from point
  (3,5) to point (1,1)

16
Another Example
// Print the largest of x, y and z public void
printMax (int x, int y, int z)

• Call printMax(7, 83, 205-52)
• Command to be executed print the largest of 7,
  83 and 205-52
• Note the method name printMax has no meaning
  to Java. It is just a string of characters. We
  could have called it aaa, pm, mymethod, etc. . .

17
Yet Another Example
// In the output window, skip a line and print //
Hello! public void printHello()

• Call printHello()
• Command to be executed In the output window,
  skip a line and print Hello!

18
Points to Remember

• A method can have zero parameters
• Syntax of a method call is name(list of 0 or
  more arguments separated by commas)

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What does the Method do?

• To find out what a method does
• Make a copy of the specification (the comment in
  the heading)
• replace all parameters by the appropriate
  arguments in the call
• This assumes the programmer wrote good comments

20
Understanding Methods

• The way we have understood these methods relies
  on comments that are
• precise
• understandable
• correct
• Your programs will be judged partially on how
  well your documentation is

21
Reading

• From now on, consult syllabus and/or webpage. We
  will try to point out appropriate readings from
  the text, but you should use the text as a
  reference when solving homework problems.
• URL http//www.cs.cornell.edu/cs100-su99

22
Assignment W1

• Series of questions requiring written answers
• Should be fairly straightforward if youve done
  the reading
• Due Thursday July 1 at the beginning of class

23
Registration Form

• Please fill out and turn in before you leave
  class today.