---
title: Eboard 19  Recursion with helper procedures
number: 19
section: eboards
held: 2017-10-06
---
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](../writeups/writeup18) 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](../writeups/writeup19) 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](../readings/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