• New partners!
  • Don't forget to introduce yourselves!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Lab.

Preliminaries

Admin

• Review sessions this week
  • Monday 8pm (Zachary)
  • Wednesday 8pm (Zachary)
  • Thursday 8pm (Erin)
  • No Sam Thursday review :-(
• I will be AFK (Away from Keyboard) starting about noon on Tuesday. If you have exam questions, ask them before then.
• I sent out notes on the prologues from exam 2. If you don't regularly read your email, you should check for those notes.
• Please don't ask tutors/mentors to answer questions on your exam code or to explain exam questions to you.

Upcoming Work

• Reading for Tuesday: Characters and Strings
• Exam 2
  
  • Exam due in electronic form Tuesday night
  • Exam due in hardcopy Wednesday class time
  • Epilogue due Wednesday night
• Today's Lab writeup (due before class Wednesday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 26 (Your Names)
  • Exercises: 1f, 3h

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery
• CS Table Tuesday, noon, White Dining Room, THERAC 25 (C)

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.
• Pun Club, Saturdays, 4pm, Way over Younker.
• Study Abroad Session, Monday the 12th 7-8pm in JRC 101. Hear about Study Abroad Experiences and think about Study Abroad.

Quiz 6

We'll look at the first problem. I'll probably return it tomorrow.

An "Interesting" Use of Recursion

You wrote something like:

(define sample-and-replace-d!
  (lambda (image left top width height)
    (let ([color1 (random-sample image left top width height)]
          [color2 (random-sample image left top width height)]
          [color3 (random-sample image left top width height)])
      (when (and (< (irgb-distance color1 color2) 50)
                 (< (irgb-distance color2 color3) 50)
                 (< (irgb-distance color3 color1) 50))
        (fill-rectangle! image left top width height
                          (irgb-average-3 color1 color2 color3))))))

We can use recursion!

      (cond
        [(and (< (irgb-distance color1 color2) 50)
              (< (irgb-distance color2 color3) 50)
              (< (irgb-distance color3 color1) 50))
         (fill-rectangle! image left top width height
                          (irgb-average-3 color1 color2 color3))]
        [else
         ; recurse on the top-left quarter
         ; recurse on the top-right quarter
         ; recurse on the bottom-left quarter
         ; recurson on the bottom-right quarter])

• Our base case is probably when width and height are small enough.

Questions

Problem 6: Two approaches

• Approach 1: Clever use of quotient and modulo.
• Approach 2: Given a row number and the number of columns, compute all the points in that row. Use map to generalize.

Question too complex to rephrase on the eboard.

> (map list (list "sam" "tyler" "bailey") (list "jones" "bailey" "doodle"))
'(("sam" "jones") ("tyler" "bailey") ("bailey" "doodle"))
> (map list (list 1 2 3) (list 4 5 6))
'((1 4) (2 5) (3 6))

How many test cases on problem 1?

I came up with something like 3 x 2 x 3 x 4 approaches. I combined some things into a test of multiple concepts. I ended up with ten or so.

Are drawings that are not renderable (e.g. because they don't have any points that fall within a typical image) still drawings?

Yes.

Should we put an example in problem 1?

Yes. Show the first few lines of it failing massively on the incorrect implementation.

Should we get rid of the ugly X's?

That would be nice. You can keep beautiful X's, though. We do judge an X by it's appearance. (No, that joke failed miserably.)

What does drawing-render! do?

Puts a drawing on top of an existing image.

You should not need it for this exam.

Should we show experiments for everything?

Yes, that's why there's a section for experiments in every problem.

Lab

Writeup: 1f, 3h