CSC 151 2019S, Class 12: Randomness
Overview
- Preliminaries
- Notes and news
- Upcoming work
- Extra credit
- Questions
- Lab
- Discussion
Preliminaries
News / Etc.
- I brought donut-like substances for my 207 class and there are leftovers.
They are fair game.
- Mentor sessions Wednesday (TONIGHT) 8-9 p.m., Thursday 8-9 p.m.,
Sunday 5-6 p.m.
- If you have not done so already, please sign and return the
class code of conduct.
- Remember: Book office hours at https://rebelsky.as.me/schedule.php
- Remember: I do take questions via email, and writing up questions can
often help you think through a problem.
- You should be getting an email about the CPUS. Let me know if you have
questions.
Upcoming work
- Reading due before class Friday
- Exam 1 epilogue due Tonight.
- Assignment 5 due next Tuesday.
- Not yet posted; should appear tonight. (Maybe sooner.)
- Your homework partner is your partner for today’s class.
- Theme: Write programs that generate “interesting” texts
(a better extension of the
sentence example for the reading).
- Flash cards due Tonight at 8:00 p.m.
- Covers Wednesday/Friday/Monday classes
- Quiz Friday: Conditionals, Preconditions and Postconditions,
Precondition checking, and Testing.
- Sample quizzes forthcoming.
- Lab writeup due before class Friday
- Exercises: 9a and 9b
- Subject: CSC 151.01 Writeup for Class 12 (YOUR NAMES)
- To: csc151-01-grader@grinnell.edu
- CS Extras, Thursday, 4:15 p.m. Science 3821: Sam talks about course design.
(Snacks at 4pm in the CS Commons.)
- Iowa Flautists in Concert. Saturday, 23 February 2019.
3:45 p.m. Sebring-Lewis Hall.
- Grinnell Symphony, Wednesday, 7:30 p.m., in Sebring-Lewis
- Men’s BBall, Friday, 3:00 p.m. vs. LFC at St. Norbert. (Hopefuly a
Saturday game, too.)
- Indoor Track and Field, Friday and Saturday, at Monmouth.
- 30 Minutes of Mindfulness at SHACS every Monday 4:15-4:45
- Any organized exercise. (See previous eboards for a list.)
- 60 minutes of some solitary self-care activities that are unrelated to
academics or work. Examples include “read for pleasure” or “take a
walk” or “make snow angels” or take a necesssary nap. Your email
reflection must explain how the activity contributed to your wellness.
- 60 minutes of some shared self-care activity with friends, such as
making a meal, having a snowball fight, or playing a board game.
Your email reflection must explain how the activity contributed to
your wellness.
Other good things
Questions
What’s the let thing in the reading?
It should not have been there. I’ve removed it.
How does roll-dice work?
It uses a technique (recursion) that we won’t learn for two weeks. Pay
attention to the what not the how.
Lab
I don’t know if it’s comforting or not, but I watched some very smart
students in my CSC 207 class inserting the same subtle error that occurs
in play-seven-eleven.
If you’re not sure how to fix the error in play-seven-eleven, consider
(a) writing a procedure (seven-or-eleven? val) that determines whether
val is seven or eleven or (b) use disjoin and section to build a
procedure that does the same.
Lab writeup: 9a, 9b
Discussion
What are the odds for winning seven-eleven?
8/36 = 0.222222222222
What are the odds of winning the badly designed seven-eleven?
6/36 + 30/36*2/36 = 0.21296296296296297
How would Sam fix play-seven-eleven?
(define seven-or-eleven?
(lambda (x)
(or (= x 7) (= x 11))))
(define play-seven-eleven
(lambda ()
(if (seven-or-eleven? (pair-a-dice))
1
0)))
Important! When possible, call another procedure, rather than
copy the body.
Good
(define ignore-then-roll
(lambda (x)
(roll-a-die)))
(define random-student
(lambda ()
(random-element students)))
Bad
(define ignore-then-roll
(lambda (x)
(+ 1 (random 6))))
(define random-student
(lambda ()
(list-ref students (random (length students)))))