CSC151 2007S, Class 32: Characters and Strings

* Welcome back!  I hope you had a relaxing break.
* I will continue to reserve time at the start of class for discussion 
  of campus issues.

Admin:
* I have finished grading exam 2.  I will distribute an answer key after
  class.
* Are there questions on Assignment 7?
* Reading for tomorrow: Files.

Overview:
* Representing text.
* Characters: The basic building blocks.
* Combining characters into strings.

==Computing with Text==
* We've done
  * Algorithms with numbers
  * Algorithms with colors
  * Algorithms with images
* But we should also be able to write algorithms that deal with text
* We need (at least) three things
  * An internal representation of text (a "type")
  * Basic procedures for working with that type (or those types)
  * Our standard Scheme techniques: Conditionals, sequencing, names, letrec,
    ...q
* Goal today: Learn types and basic procedures
* Two basic types:
  * Strings (e.g., text)
  * Chararacters, building blocks of strings

==Characters==

* Represent character constants with obscene notation.  To talk about the
  letter a, we can't write a (looks like a name to Scheme), can't write
  'a (a symbol), can't write "a" (a string), so we write #\a
  * One character strings are represented differently than single characters
  * Perhaps because we compute with them differently.
* In the internal representation of characters, there is a sequence of characters
  We call it the "collating sequence"
  Because we have this sequence, the computer can think of each char as a
  number
* You can see a list of ASCII characters by opening a terminal window and
  typing

  man ascii

==Strings==

* 0-based sequences of characters
* Constants represent with double-quotation-marks
  "triskaidekaphobia"