• New partners! Please grab a card to identify your computer.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • About Quiz 1.
  • Questions.
• Lab.
• Debrief (if time).

Preliminaries

Admin

• Happy Labor Day!
• The grader email has been fixed.
• Quiz 1 returned. If you had trouble on part 1, please try to speak with me. We'll talk more about it in a few minutes.
• I've added additional office hours at 8:30-9:00 MWF to give you more opportunities to speak with me. Still bookable at https://rebelsky.youcanbook.me.

• Before today's lab (and perhaps before every lab you do for the next week or so), please type the following command in the terminal window.

  /home/rebelsky/bin/csc151-update
  

Upcoming Work

• One reading for Tuesday: Transforming Images
• Assignment 2 due Tuesday at 10:30 p.m.
  
  • I will take questions on the assignment at the start of class today and Tuesday.
• Lab writeup (due before class Wednesday)
  • Email to grader-151-01@cs.grinnell.edu (not to me; don't forget the cs).
  • Subject: CSC 151 Lab Writeup Class 6 (Your Names)
  • Problems:

Extra Credit Opportunities

Academic

• Tuesday, noon, CS Table, JRC 224C. Mobile networks in developing countries.
• Convocation, Thursday at 11am, JRC 101.
  
  • Sam's convocation spiel.

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 1:30 and Mondays at 4:45. Requires sign up in advance.
• Pun Club, Saturdays, 4pm, Way over Younker

Notes on Quiz 1

• Quizzes are ...
  • An opportunity for me to discover what you do and don't understand.
  • An opportunity for you to discover what you do and don't understand.
  • An incentive for you to review materials.
  • Intended to be relatively "low stakes".
• Note 1: Every real number in DrRacket is also rational.
• Note 2: ceiling gives an inexact output when given an inexact input.
• Note 3: Although I think of the card as the input to the algorithm in problem 2, I accepted anything that was argued well.

Questions on HW2

Is it okay that we don't have 0's after the decimal point for 2.5 or something similar?

That's fine. You can't force DrRacket to give you 0's at the end of an inexact number.

Should we do one or two computations for computing total minutes and total seconds?

Two separate computations.

How should we submit?

Ideally, you will copy and paste from wherever into the body of an email message.

What about the "how to add" part if we have pictures?

If you don't have pictures, copy and paste is better.

If you do have pictures, an attachment is okay.

Should we include the interactions when we try different contestants?

Yes.

Additional Questions

Lab

• Brighter numbers have higher component values. This seems counterintuitive until you realize that it's more light rather than more paint.
• Components are capped at 255. If you use a component larger than 255, you end up with 255.
• No lab writeup

Debrief - Some Points from Your Mentors

• Scheme model: Open paren, procedure, arguments, close paren
  • (+ 2 3)
  • (+ (2) (3))
• Procedures almost always appear immediately after an open paren
  • Exception: When used with o
• Sequencing: Scheme evaluates expressions inside out, which can seem backwards.
• There are different kinds of values:
  • Strings - surrounded by quotation marks
  • Numbers of all sorts
  • Images - represented by integers
  • Color - represented by integers
  • The value 1, could be one, or an image, or a color, ...
  • The value 123215413112 could be a large integer, or a color, or an image
• You can name things with define
  • (define gold (color->irgb "gold"))
  • (define golds (color-swatch gold (irgb-darker gold) (irgb-lighter gold)))
  • (image-show golds)