CSC153 2004S, Class 12: Strings

Admin:
* Questions on homework 3?
* Homeworks 1 and 2 to be graded tonight
* Talks today at 2:15 and 4:30 (Extra Credit)
* Exam 1 assigned
* Read "Pairs and Pair Structures"

Question on Homework 3
* What kind of precondition checking should we do?
  * For example, in win (or whatever it's called), verify that both parameter lists contain only symbols, and that those symbols are legal scoring values.
* Can we use our typechecking procedure?
  * Sure

Questions on Exam
* How does it differ from a homework?
  * You may not talk to others about it
  * You must turn in a printed copy
  * It's probably harder
  * Guaranteed minimum grade for particular time spent
* How is it similar?
  * You do it on your own time
  * You can use reference materials
  * You can ask questions in class

Overview:
* Quick introduction
* Lab

Observation:
* There are many ways to interpret *cat*
  * The name of something (e.g., a value, a procedure) 
	(define cat ...)
  * A symbolic value 
	'cat
  * The sequence of letters c, a, t
	"cat"
* Sequences of letters are called "strings" and are surrounded by double quote marks (as in "strings" earlier on this line)
* The elements of those sequences are called characters: #\a #\A
* Why are strings useful?
  * Versatile: Can permit different "types" of information (which must then be parsed)
  * Manipulable: Concatentate two strings; Eliminate part of it
  * Manipulate collections of strings: Sort
  * "Natural" way to represent lots of information
  * Programs may need to reflect "actual words"
* How do lists and strings relate?
  * Both are ordered collections of values
  * lists can contain any kind of values
  * Strings contain only characters
  * Some applications naturally call for a string
  * Easier syntax for strings (#\c #\a #\t) vs. "cat"
  * Scheme provides operations for converting between the two
    (string->list "cat") => (#\c #\a #\t)
    (list->string (list #\c #\a #\t)) => "cat"
* Scheme provides lots and lots of operations for dealing with characters and strings.  
  * Learn through practice.

* Try the lab, ask good questions