CS 100, Summer 2001
Thursday, 7/5
Lecture 7
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Announcements: 
+ Assignment 2 due Friday (7/6)
+ PRELIM 1 on Monday (7/9): covers Savitch Ch.1-3, all lectures, exercises, assignments 1 and 2
+ Leave office hours as is - if you cannot make them, please make an
  appointment by email
+ reading for tomorrow: bring questions!
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Some random issues:
- print vs. println (includes newline)
- error in PrimeNumbers.java: Algorithm description
  should check div for 2 to checkNum.
- results of minute paper
  - I'll start bringing printouts of code examples to class
  - declaring int more than once inside a loop: this is ok!
    but it may not be what you expected -
    it's a different variable each time through the loop.
    (we'll talk about scope later today, maybe)
  - most confusing: Matlab and methods.  This is unsurprising, since
    both were covered very quickly and shallowly!  More today.
- Ben's post on random and his comments on Ex 4 are *required reading*.
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Topics:
+ SpaceInvadersDoWhile 
+ named constants
+ Matlab 
+ methods 
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+ assignment: named constants
  - use variables for commonly used numbers (classic example is pi)
  - style: improves reuse and readability
  - but not truly constant because you could reassign
+ can make variables "unvariable" with $final$:
  $final$ type variable = value 
  - final varibles known as CONSTANTS
  - won't be able to reassign a constant
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- to further refine our view of loops...
  - note do-while in SpaceInvaders requires some extra checks
- for: MirrorNumber?
  - don't be intimidated! 
  - do read it.  Anyone have questions??
- style: add // comments if closing brace is far from opening brace.  
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MATLAB
+ DIS tutorial, part 1 (matlab1.m)
  - you know enough know to pick up what's there much more easily
  - same issues: variables, operators, strings, simple functions
  - we won't go into MATLAB in depth here, but welcome questions
  - later, we'll talk about conditional statements and loops in MATLAB
+ using a semicolon in Matlab
  - if you don't, you'll see the "result" of your command
  - if you do, the output is suppressed
  - both are fine.
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+ Methods
- think function: name(inputs)  ->    generates output
- three parts: input, processing, and output (same as with algorithms!)
- methods allow you to "delegate" work and tend to shorten the program
- examples:
  - "open the door" method (no input; action: opening door)
  - "read this book" method (input: book, action: reading)
  - "take this money and buy my groceries for me" method: 
    (input: money, grocery list; action: purchasing, transport back; 
     output: groceries (and change!))
- without programming:
      ____
    \/ 4    => 2

  method:
    sqrt(4) => 2

  4 is the input/argument/parameter
  2 is the output/returned value

- the action of performing the function/method: INVOCATION/CALLING
  NOTE: the returned value REPLACES the invoked function
        how? what about sqrt(4) + 3 ? 
        you would add 2 + 3 -> 5
        so, the 2 replaced sqrt(4)
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Examples in Java:
  Math.random(): see also random.java
  System.out.println(_stuff_);
  System.out.print(_stuff_);
  main(String[] args)
+ interesting features:
  - not all have inputs
  - some don't actually give a value (just perform an action)
+ 2 general kinds:
  - performs action without returning a value
  - returns value (and maybe also performs action)
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How to use:
+ perform action:
  System.out.println("Hello");
  
  note: common source of confusion: output is NOT a returned value
  e.g., try 
	int x = System.out.print("Hello");
+ return a value:
  int x = Math.random()*10;
+ order of actions for operations that use methods (Control Flow of Methods)
  - Java invokes methods
  - replaces method call with the returned value
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How to design your own methods:
+ put your method before the main() method
+ invent a name
+ decide on the inputs to the method
+ write tasks for BODY of method (what the method does)
+ decide if there's a value to return
+ add comments before the method that indicate
  a) what it does
  b) what the inputs are
  c) what the output (return value) is 
EXAMPLE: Methods.java

+ control flow:
  - Java starts at main() in Main Class (assuming you set Main Class target)
  - Java works top-down, statement-to-statement
  - the myPrint call:
    o do expressions in methods (follow precedence, associativity)
    o do method call
    o find myPrint
    o check if type of input matches expected type
    o "bind" arguments to input variables (so "Kiri" gets "bound"
      to "s")
    o perform actions in invoked method
    o return a value (if specified)
  - return control back to the point when/where method was invoked

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* pick up graded Exercise 4.
* bring questions for TA review tomorrow!