CSC 151.01, Class 11: Boolean values, predicate procedures, and list filters

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Notes from quiz 3
• Lab
• Debrief

News / Etc.

• New partners.
• Please switch driver and navigator after every problem.
• Please make sure to return your computer cards to the jar.
• Thank you for all of the excellent exam questions. You will find many Q&A in the exam.
• I did not have time to finish grading your quizzes this weekend. We will still go over them to help you understand what I expect for documentation and tests.

Upcoming Work

• Writeup for class 10 due TONIGHT at 10:30 p.m.
  • Exercise 6
  • To: csc151-01-grader@grinnell.edu
  • Subject: CSC 151.01 Writeup 10 (YOUR NAMES)
• Writeup for class 11 due Wednesday at 10:30 p.m.
  • Exercise 4c
  • To: csc151-01-grader@grinnell.edu
  • Subject: CSC 151.01 Writeup 11 (YOUR NAMES)
• Read: Local bindings for Wednesday’s class.
• Read: A computer scientist’s perspective of data science for Wednesday’s class [Should be ready late tonight].
• Exam 1
  • Exam due TOMORROW night
  • Cover sheet due Wednesday in class
  • Epilogue due Wednesday night

Extra credit (Academic/Artistic)

• CS Table, Tuesday at noon in PDR A: Activism
• CS Extras, Thursday at 4:15 in 3821, Study Abroad

Extra credit (Peer)

• Women’s soccer, Saturday
• Women’s soccer, Sunday

Extra Credit (Misc)

None at the moment.

Other Good Things

Exam questions

Can you give me a hint on problem 2?

Don’t use substring

In the lab in which we had 42,000 things to deal with, I asked you to find the middle 5. How did you do that?

On problem 1, do we have to support complex numbers as input?

Yes.

How do I generate a random six digit number?

(random 1000000)

How do I submit my exam?

Name it 012345.rkt (substituting your random number)

Send it to rebelsky@grinnell.edu as an attachment in an email message entitled “CSC 151.01 Exam 1” (or something similar)

Can you explain the parameters to sublist?

Starting position (inclusive) and ending position (exclusive), just like in substring

Can I use the sublist procedure I wrote in problem 2 for problem 5?

Sure.

Can I use string-length?

Sure.

How should we write our examples or tests?

You know how to write tests.

Examples you will generally run in the interactions pane and then copy and paste the input/output to the definitions pane and then comment it out.

Notes from quiz 3

Part a: Documenting nearest multiple

;;; Procedure:
;;;   nearest-multiple
;;; Parameters:
;;;   val, a real
;;;   n, a real
;;; Purpose:
;;;   Find a multiple of n that is nearest to val.
;;; Produces:
;;;   m, a real - a multiple of n
;;; Preconditions:
;;;   n is not zero
;;; Postconditions:
;;;   * m is a multiple of n.  That is, m/n is an integer.  (Alternately,
;;;     the remainder of m/n is 0.) (There exists an integer i, such that
;;;     m = i*n)
;;;   * m is a nearest multiple of n to val.  That is, for all other
;;;     multiples of n, h, the |h - val| >= |m - val|

• Don’t rename the parameters to meaningless things, such as value1 and value2
• If you do want to rename them, choose more meaningful names.
• We always name the result in the Produces section.
• We always give a type in the Produces section
• We might add an additional note in the Produces section
• If we don’t know what a multiple is, we might say “7 is a multiple of 2 because when I multiply 2 by 3.5 I get 7.”
• the distance of h to val is no smaller than distance of m to val. By “distance” we mean the absolute value difference between the two values.
• Sam would call n an integer, but it’s up to you.
• What’s the nearest multiple of 4 to 10? (val is 10, n is 4)

Part b: Testing

• Different tests! (That is, test different concepts)
• Make sure that your tests test valid inputs and outputs.
  • If there are two nearest multiples, don’t assume one.
  • If zero is not a valid n, don’t use it as n.

Lab and Debrief

How should I compare the two-letter state abbreviation to “IA”?

= - No. They are not numbers. = is for numbers

eq? - No. eq? does not always work the way you expect for strings.

eqv? - No. eqv? does not always work the way you expect for strings.

equal? - Yes. equal? works well as your default comparison.

string=? - Yes. You know that they are strings.

string-ci=? - Yes. And this is nice because it supports "ia".

Can I write a lambda-free solution to in-iowa?

Sure.

First we extract the state. (section list-ref <> 4).

Next we compare to “IA”. (section string-ci=? <> "IA").

So we can just compose those two. (o (section list-ref <> 4) (section string-ci=? <> "IA"))

Is there an easy way to write “between a and b”?

(section < a <> b)

How do I figure out if any city in IA lacks a longitude?

(filter (negate has-longitude) (filter in-iowa? zips))