CSC153, Class 13: Characters and Strings

Overview:
* Different types
* Characters in Scheme
* Strings in Scheme
* Lab

Notes:
* Take-home exam Wednesday.  Due the following Wednesday.
* Yes, I plan to have homework 1 graded by then.
* Are there questions on variable-arity procedures?
* How many of you know HTML?
* Readings for tomorrow: HTML, CGI
* All-campus forum, noon ARH 102

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Question: How do you document variable-arity procedures

;;; Parameters
;;;   required: an integer
;;;   optional-1 ... optional-n: 0 or more integers

Question: Is there a nice way to display one of the variables?
   E.g. "You bozo, "hello" is not a number"
Answer: Sure, as long as you're willing to try to convert
  the value to a string.  (More info today.)

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Types in Scheme

Consider i.  What could it be?
* The square root of negative 1. 
  (sqrt -1)  
  0+i
* The name of something.
  (define i (lambda (x) x))
  i
* A character: Something that makes up strings
  Something you can type on the keyboard
  #\i
* A string of length 1
  "i"
* A symbol 
  'i

Scheme, like most programming languages, necessarily provides
different notations (names) for the different kinds of values

What can you do with characters and strings in Scheme?
* Build new strings from old with string-append
  (string-append "Hi, " + student)
* Build new strings from characters with
  + (make-string NUM CHAR)
  + (string CHAR1 CHAR2 CHAR3 ... CHARN)
* Build string literals with double quotes
* Extract information on strings
  + A particular character with string-ref
  + Length with string-length
  + Substrings with substring (a chunk of the string)
* Compare strings

More stuff than I want to tell you about.

Do the lab.

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REFLECTION

* test, as I've written it, doesn't always give what you'd expect

* How did you compare digits to uppercase?
(char->integer #\A)
(char->integer #\9)

or 

(char<? #\A #\9)

* Is that enough testing?

* #\space vs #\ 

* '\' is pronounced "backslash"
  '/' is pronounced "forward slash" or just "slash"
  '#' is pronounced "pound"
  '!' is pronounced "bang"
  '~' is pronounced "tilde" (although some call it "twiddle")
  '&' is pronounced "ampersand"

* string-append can take lots and lots of parameters

* How would you write 'last-char'?