CSC151.01 2006S, Class 07: Characters and Strings

Admin:
* Groups continue from yesterday.
  Since Mr. Wood is not available on Tuesdays, 
  Mr. Thompson will work with Mr. LaRue and Mr. Bonnin 
  Cadogan.
* I will record attendance on the eboard.  If you object to your name
  appearing in this context, please let me know.
* Assigned: HW4.
* Reading: Writing Your Own Procedures
* Due: HW3.
* Extra credit: 
  * Tuesday extra (Today 12:45-2:00 p.m. in Science 2424)
  * Convo (11-noon, Thursday, Herrick)
  * Blood Drive on Friday
  * Other announcements?

Overview:
* Additional lessons from yesterday.
  * What did you think of "Round Robin Review"?
  * Think about how your windows are arranged.
  * Think about how you explore procedures.
  * Think about how you interact with DrScheme.
  * More on modulo vs. remainder
* Questions on the readings?
* Lab.

/Lessons from Monday/

* What does quotient do?
  * It divides two numbers and gives you back a whole number without a remainder
  * Correction: It divides two *integers*!
  * Exact or inexact?
* Moral one: You should check these things.
* What's the relationship between remainder and modulo?
  * They deal with negative numbers differently.
  * modulo takes two numbers and figures out how much is left over (how much you have to add or subtract) after you divide the first by the second
  * remainder will only add
  * Background: modulo is a mathematical concept
     a is equivalent to b mod c if (a-b) is evenly divisble by c
  * Rule in Scheme: modulo returns a value of the same sign as the divisor
    Given X and Y, express X as q*Y + r
      0 <= r < Y
    Suppose X=5 and Y is 2, X=3*2 + -1 (q=3, r-1)
    For modulo, we want the sign to be the same.
    -|Y| < r < |Y|

TYPO IN READING

'number-->gt;string' should be 'number->string'
  (Sam sometimes get HTML formatting wrong.)

For those who asked, #\31 is "The unit separator", a funky
control character.