CSC151, Class 19: Numeric Recursion

HAPPY BIRTHDAY AMANDA!

Overview:
* Questions and answers on list recursion
* Questions and answers on numeric recursion
* Lab

Notes:
* I'll be gone on Friday.  Mr. Stone will be teaching the class.
* No new reading for Friday.
* Exam 1 distributed.  The content of the problems is unlikely
  to change.  The wording may.
* Comments on class? EBoards? Web site?
* Notes on writeup 1.

3.14

(define pi 3.14)
(define sams-gpa 3.14)
....

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Confusion about the six P's

Procedure: Names the procedure
Parameters: Names and types the parameters
Purpose: A few sentences giving the intent
Produces: Names and types the result
Preconditions: What must hold in order for your procedure
  to work reasonably (in addition to the typing).
Postconditions:
  Guarantees about the result
  "Returns a number"
(define square (lambda (x) 1)

Procedure:
  swap-first-two
Parameters:
  lst, a list with at least two elements.
Purpose:
  Build a new list that resembles lst except that the first
  two elements are swapped.
Produces:
  newlst, a list
Preconditions:
  [See above]
Postconditions:
  lst is unchanged
  (list-ref newlst 0) is the same as (list-ref lst 1)
  (list-ref newlst 1) is the same as (list-ref lst 0)
  (list-ref newlst x) is the same as (list-ref lst x)
    "for all other reasonable x"
    for 2 <= x < (length lst)