CSC151.01 2006S, Class 08: Procedure Definitions

Admin:
* Absent: Wood (excused), Zamora
* Same week -> Same groups
* Are there questions on the lab?
* Are there questions on the homework?
  * What should I do with number?  Well ... you need strings so ...
* Reading for Friday: Boolean values.
* EC: Osgood at 11 a.m. tomorrow.

Overview:
* Why define your own procedures?
* How to define your own procedures.
* Lab.
* Reflection

What are the components of an algorithm?
* Basic data and operations on them
  * Lists, symbols, numbers, characters, strings, procedures
  * About a dozen or more operations each
* Naming things
  * (define name thing)
* Sequencing operations
  * Give them in order (in the definitions panel before the "run")
  * The arguments to a procedure call are evaluated in some sequence
    (+ (* 2 3) (sqrt 2))
* Make choices - Not yet
* Repeat - Not yet
* Define "subroutines" - Today's topic

Subroutine: You want to do something similar multiple times, but perhaps
with different data
* Simple strategy: Copy and paste and update
  * Sometimes you get it wrong (you forget to update everythjing)
  * Sometimes you get the initial code wrong
  * Also hard to read
* Better strategy: Name and Parameterize code

* Form
(define NAME-OF-PROCEDURE
  (lambda (PARAM1 PARAM2 ... PARAMN)
     THE-CODE-YOU-WANT-TO-NAME))

/Notes/

* You do /not/ need to document (unless I tell you to do so).
* Do not do problem 3.c
*
  (define root1 (/ (+ (- b) (sqrt (- (* b b) (* 4 a c))))
                   (* 2 a)))