CS151, Class 12: Strings

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

Notes:
* Concerns about time in class.
* Are there questions on Booleans and conditionals?
* Are there questions on the writeup?

Questions on Homework

* .ss or .scm
  I DONT CARE
* Distinguishing between rationals and reals
  We'll say that rationals are exact and reals are inexact
  (if (and (rational? val) (exact? val))
      'looks-like-a-rational-to-me
      'looks-like-something-else)
* Why does (and num1 num2 ... num3) return num3

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There are many different possible interpretations of i
* Variable i, naming some other value
(define i 5)
(define i (list 5))
* Atomic symbol i, reprsenting some concept (e.g., self)
'i
* The letter you can type on the keyboard, representing
  part of a word
#\i
* An i can be the imaginary part of a complex number
0+i
* Variation of variable: Can be an argument
(define foo (lambda (i) ...))
* One of the other kinds of i, as part of a list
(list i) or (list 'i) or (list 0+i) or (list #\i)
* The one-letter word i

Sam tries to resolve confusion by swtiching to "cat"
* 'cat - an abstract concept
* cat - names some value or names some function
* "cat" - the sequence of letters #\c #\a #\t

In most languages, it is helpful to be able to speak about
both sequences of characters (which we call strings) and
single characters

In Scheme, single characters start with #\, strings are surrounded
by double quotation marks

#\a

"Sam"

What can you do with characters and strings?
* Compare them to each other
Perry
Rebelsky
Cook
Stoltzfus
* Build strings
  + From characters (string #\a #\b #\c) -> "abc"
  + From other strings 
(define student-to-pick-on "Andy")
(string-append student-to-pick-on ", is this clear?")
-> "Andy, is this clear?"

Can you use string append on characters?  No!
(string-append "student" (string #\s))
(string-append "student" "s")
-> "students"

The following is illegal and is retained in the eboard only
fior discussion purposes.
(string-append ("student") (string #\s))

* Get information about strings:
string-length
substring
etc.

Do the lab

WARNING

control-char? should take a character as a parameter!