CSC 151.03, Class 19: Recursion with helper procedures

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Basics of helper recursion
• Tail recursion
• Why use tail recursion?

News / Etc.

• New partners.
• Please make sure to return your computer cards to the jar.

Upcoming Work

• Writeup for class 18 due TODAY at 10:30 p.m.
  • Exercise 5
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 18 (YOUR NAMES)
• Writeup for class 19 due Monday at 10:30 p.m.
  • Exercise 4
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 19 (YOUR NAMES)
• Reading for Monday’s class: List recursion, revisited
• Exam 2 prologue due TONIGHT at 10:30 p.m.
• Exam 2 due Tuesday at 10:30 p.m..
• Exam 2 cover sheets due Wednesday at the start of class
• Exam 2 epilogue due Wednesday at 10:30 p.m.

Extra credit (Academic/Artistic)

• Nice Fish
• TODAY, 4:15 p.m. Poet talk
• “Sita Sings the Blues,” at 3:30pm on October 8 in the Gallery

Extra credit (Peer)

• Open Mike Comedy, Friday, 8pm, Main Lounge. Pizza.
• RTS, Loose Lounge, Friday, 9:30 p.m.
• Fun Palaces, Saturday, 1-3, Bucksbaum Rotunda. Come and make art.
• SOL’s Latin American Festival, Saturday, 6-8pm, Sebring Lewis
• Neverland players

Extra credit (Misc)

• Any Fall Fest Event

Other good things

• Volleyball vs. Beloit, Friday at 7:00 p.m.
• Women’s Tennis vs. St. Norbert, Saturday at 9:00 a.m.
• Volleyball vs. Lake Forest, Saturday at 1:00 p.m.
• Women’s Tennis vs. Ripon, Saturday at 3:00 p.m.
• Football, Saturday at 1:00 p.m.
• Lunar Festival Tonight (?), 6:20 p.m. Harris Gym

Friday PSA

• I know you are stressed.
• Working out is good.
• Watching TV (or, better yet, a play) is good to have your mind relax from its stresses.
• If you are of legal age, consumption may be appropriate.
• Playing in giant hampster balls can generate joy.
• Etc.
• Whatever you do, please do it in moderation. I do not want you to damage yourself.
• If you cohabit, consent is absolutely, positively necessary. I do not want you to damage another person.

Questions

On problem 1, can both start and finish be negative?

Yes.

On problem 1, do I have to deal with the situation in which finish is less than start?

No, not if you disallow it in the preconditions.

On problem 2, does it matter what order we get the points?

No. However, I would like it to be systematic.

For problem three, should we match your ordering and choice of adjectives?

Yes.

Quiz

This week’s quiz is fun. Next week’s quiz is even better. Identify your classmates!

Lab

Please discuss which switching format you and your partner will use

• Switch every ten minutes
• Switch midway through class
• Switch every problem

We will debrief on the lab on Monday.

Here is some sample output for 2b.

> (my-quotient (list 3))
3
> (my-quotient (list 3 5))
3/5
> (my-quotient (list 3 5 7))
3/35
> (my-quotient (list 3 5 7 6))
1/70
> (my-quotient (list 3 5 7 6 1/10))
1/7

When you hit #4, please hit shift-reload.

Writeup: Exercise 4