Welcome to CS 100

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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!

CS 100
Lecture 1
1
Course Staff
Instructor: Lynette Millett, [email protected]
 TAs:

– Wei Tsang Ooi, [email protected]
– Alan Renaud, [email protected]
– David Welte, [email protected]

Consultants:
– Rocky Chen, [email protected], Young Ho
Cho, [email protected], Amanda Waack,
[email protected]
CS 100
Lecture 1
2
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

CS 100
Lecture 1
3
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
CS 100
Lecture 1
4
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.
CS 100
Lecture 1
5

Main Concepts Today
What is an algorithm?
 Method and method call
 Reading this week: Chapter 1 (skim),
Chapters 2 and 3
 Handouts

CS 100
Lecture 1
6
Algorithm

A set of instructions for performing
some task that is:
– precise
– unambiguous
– effective
– abstract

In other words: well-specified
CS 100
Lecture 1
7
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

CS 100
Lecture 1
8
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
mother’s maiden
name and attact first
3 letters of
hometown
CS 100
Lynette Millett born in
Norway, ME to I.
(Rogers) Millett
becomes:
Mil+Ly = Milly
Ro+Nor = Ronor
Lecture 1
9
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. . . .

CS 100
Lecture 1
10
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 they’re
told or, worse, something undefined
 Precision is important
 Any other ambiguities in that example?

CS 100
Lecture 1
11
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, |||
CS 100
Lecture 1
12
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, what’s a method?
 “Method”, “procedure”, “function” often
used interchangeably

CS 100
Lecture 1
13
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
CS 100
Lecture 1
14
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)
CS 100
Lecture 1
15
Another Example
// Print the largest of x, y and z
public void printMax
(int x, int y, int z)

Call: printMax(7, 83, 20*5-52);
Command to be executed: print the
largest of 7, 83 and 20*5-52
 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. . .

CS 100
Lecture 1
16
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!”
CS 100
Lecture 1
17
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
)
;

CS 100
Lecture 1
18
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
CS 100
Lecture 1
19
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
CS 100
Lecture 1
20
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

CS 100
Lecture 1
21
Assignment W1
Series of questions requiring written
answers
 Should be fairly straightforward if
you’ve done the reading
 Due Thursday July 1 at the beginning of
class

CS 100
Lecture 1
22
Registration Form

Please fill out and turn in before you
leave class today.
CS 100
Lecture 1
23
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