• New partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Exam Note.
  • Questions.
• Lab!

Preliminaries

Admin

• I hope you had a great family weekend, whether or not your family was able to visit.
• I mourn those of you who have become members of the undead.
• Review sessions
  • Wednesday at 8pm (Kumar)
  • Thursday at 10am (SamR)
  • Thursday at 8pm (some zombie)
• For the first time in a long time, I was unable to get the CSC 151 quizzes or exams graded over the weekend. A few other tasks with tight deadlines are coming up, so you probably won't get the exams back until Friday.
  
  • I apologize.
  • I will get your quizzes back to you tomorrow. We'll also discuss them.

Upcoming Work

• Reading for Tuesday: Anonymous Procedures
• HW 4 due Tuesday night.
• Today's Lab writeup (due before class Wednesday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 18 (Your Names)
  • Exercise: 3c

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery.
• EE's show in Smith
• CS Table: YouTube Content Identification.

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance.
• PALS dinner Thursday night. (Sam will treat if you find it a financial burden.)
• Pun Club, Saturdays, 4pm, Way over Younker.

An Exam Note

What should I do if I got the following as sample output on problem 3?

> (seconds (add-times (time 0 0) (time 0 97)))
37
...
> (seconds (add-times (time 0 0) (time 0 97)))
97

• The same procedure shouldn't give two different answers.
• In at least one case, it's not correct.
• One of the answers is probably not representative of the actual code.
• Maybe it was cut and paste (from the exam).

Excuses

• They generated the two outputs with different versions of the procedure.
• It must be accidental; no one would ever be stupid enough to forge output for Sam (or any other computer scientist).

Questions

These can be on the homework, the reading, whatever.

Can we use helper procedures?

Certainly?

How much documentation should we use for helper procedures?

Preferred: Six P's.

Because Preconditions/Postconditions are Painful Conditions, I'm okay with the 4P's.

But because I primarily care that you think about inputs and outputs and what the procedure does, I might accept a variant. (You'll find that most acceptable variants aren't much shorter than the 4P's)

We think our code should work and it doesn't. Why not?

Please send it to me and I'll see what I can figure out.
HELP NEEDED on HW4 is a good subject.

What radius should our circle of shapes be?

Whatever you find most convenient.

Why didn't people ask those questions at the start of class?

I don't know.

Lab

Writeup is 3c

What's better?

(define irgb-brighter?
  (lambda (color1 color2)
    (if (> (irgb-brightness color1) (irgb-brightness color2))
        #t
        #f)))

(define irgb-brighter?
  (lambda (color1 color2)
    (> (irgb-brightness color1) (irgb-brightness color2))))

ZS says "If you find yourself explicitly writing #t and #f, you can probably write a better version!"