CSC151.02 2015S, Class 04: Computing with Symbols and Numbers
=============================================================

* New partners!  (For today and tomorrow.)
* Don't forget to introduce yourself.

_Overview_

* Preliminaries.
    * Admin.
    * Upcoming Work.
    * Extra Credit.
    * Questions.
* Topical Review
* Lab

Preliminaries
-------------

### Admin

* Office Hours:
    * Normally: 10:00-11:00 MTWF, 3:15-4:00 M
    * Currently booked: 10:30-11:00 M, 10:45-11:00 Tu, 10:00-11:00 F 
    * Reserve a slot at <https://rebelsky.youcanbook.me/>.
* Don't forget to say your name when you ask or answer a question so that
  the mentors can record.
* How many people would use lab tutors on Sundays from 3-5 pm if we added
  a shift then?
* Mentor sessions Mondays at 7pm and Thursdays at 8pm in the Commons.
* The "Current Reading" link doesn't always work.  If it seems to be way
  too familiar, check the syllabus.
* Homework comments:
    * My goal is that homework should be no more than three hours.  If
      you're finding that it's taking much more (or that you're on track
      to take much more), you should talk to me.
    * Submit *one* assignment for each group.
    * Separate prologue and epilogue.
    * Subject: "CSC 151.00 Assignment 2 (Person One, Person Two, Person Three)"
    * I hear that getting three Grinnellians together is hard.  I'll shoot
      for partners on most remaining assingnments.

### Upcoming Work

* [Assignment 2](../assignments/assignment.02.html).
    * Due Tuesday at 10:30 p.m.  
* Lab writeup for lab 3, due tonight at 10:30 p.m.:
  <http://bitly.com/151-2015S-lab03>
* Lab writeup for lab 4, due Wednesday at 10:30 p.m.: Problem 2, parts d,e,f.
  <http://bitly.com/151-2015S-lab04>
* Reading for Tuesday:
    * [Drawings as Values](../readings/drawings-reading.html)

### Extra Credit Opportunities

#### Academic 

* Friday, 12:10 p.m., JRC 224A (Day PDR), CS Table, "Redundant
  Arrays of Inexpensive Disks" (copies outside my office)

#### Peer Support (Afternoon Section)

* Men's Baskeball, Tuesday, 7:00 p.m., New Darby
* Meditation group, Wednesday, 9:00 p.m., CRSSJ
* Swimming, Friday, January 30, 6:30 p.m., Osgood Natatorium
* Swimming, Saturday, January 31, noon, Osgood Natatorium
* Men's Tennis, Saturday, January 31, Field House

### Recommended Events (no EC unless mentioned above)

* Women's Basketball, Tuesday, 5pm, New Darby
* Belly Dance Club, to be scheduled
* Salsa Club, Tuesdays at 7pm and Saturdays at 2pm
* Meditation group, Wednesdays at 9:00 and Sundays at 4:00 in CRSSJ
* #OneGrinnell, Wednesday, February 4 at 4:15 p.m.

### Questions

Topical Review
--------------

Model:

* Two minutes with your partner.  
    * What were the main points of the reading?
    * What were the more difficult things to understand?

Main Points

* Scheme accepts a variety of types of numbers: integers, real, complex
* Scheme has symbolic values, which you indicate with a single-quotation
  mark.  We use that mark to distinguish them from names.

Difficulties / Questions

* What's the difference between modulo and remainder.  Do the lab.
* What's truncate? Do the lab.
* Why is `(sqrt 2)` rational?  I'll answer at the end of class.

Lab
---

_Why is `(sqrt 2)` rational?_

> It comes from a number of design decisions in the Scheme language.
  `(sqrt 2)` is approximated ("inexact", in Scheme terms).  If it's 
  approximated, it's representable as a ratio of two integers.  Hence,
  it's rational.