Tues Sep 9 Lecture Notes
 (We'll see how much of this we cover and where we go.)

 * Questions?

 * Ground rules
   * ==> ask questions <== to slow me down.  Please don't be shy.
   * Many of my examples will be unix-ish.  
     That's just what I'm most familiar with.  Your mileage may vary.

 * This first part of the course - and the first three chapters - 
   are trying to give you a taste to get you going; 
   we'll go slower and more systematically in a bit.

 * The name of the game is  ====> debugging. <====
   Expect your programs to fail most of the time.  That's normal.
   Your goal isn't to write perfect programs the first time;
   instead you're trying to learn to be a detective,
   finding out what's wrong by whatever it takes: 
   trial and error, leaps of intuition, elimination of all other
   alternatives, or even peaking behind the curtain if necessary.

 * Running an editor and saving a text file
    
   * Note that ome window systems will hide extension (.txt, .pl, ...)
   * Do some demos in class.
   * Most of these editors will require some set-up;
     I haven't had time to get all the lab computers "just so."

   * XEmacs or Emacs : 

         * All commands can be reached by typing their name after Meta-X.
             * Note particularly
                 * Meta-X c-perl-mode
                 * Meta-X font-lock-mode
             * "Meta-X" means either 
                 * escape-x, or 
                 * hold down meta key and type x
             * Don't type the whole command; press "tab" for auto-completion.

         * Type "control-h" for help.  Then "t" for tutorial.

         * control-x 2  - splits the window vertically.
         * Meta-x shell - start a command shell within a window.

   * TextPad :

         * Perl mode needs to be "added".  (I forget the menu item.)
         * Standard perl file endings are .pl and .pm
         * You can also run the compiler from within textpad.

 * perl -de1

   * an idiom to get you to a place where you can type perl code
     and see it execute line by line.
   * (Do this in class.)

 * #!/usr/bin/perl  - what's that all about?
   
   $ chmod +x program.pl   (on unix)
   $ ./program.pl

 * Getting Help

   * at the command line:  
        * "man perl" and the many others like "man perlfunc"
        * perldoc

   * online at www.perldoc.com

   * online at www.perlmonks.org - many tutorials and examples.
        * But please don't ask them to do your homework for you.
        * aside: plaigarism vs open source vs re-inventing the wheel

   * index in the back of the text

   * index in the Camel

   * email me : mahoney@marlboro.edu

 * How Computers Work - an overview
   * They work great :)        
     (Have you seen the little sideways smiley before?)
   * Feel free to chime in; I'm not sure where you all are.
   * Ideas include
      * memory (various kinds) vs cpu vs disk "files"
      * bits, bytes, powers of 2 : kilo, mega, ...
      * clock speed and data bus
      * logic : and,or, and all that
      * data  : int, float, ASCII char, string, ...
      * other models - parallel, analog, ...
      * Turing machine
   * ... there's lots to say here, we'll see how much we want to do.

 * How to write computer programs.
   * Think before you code.
   * Describe in writing the inputs and outputs.
   * Test everything.  (Many people code the tests before the program.)

 * Comments and documention.
   * Header describing how it runs, who wrote it at the top of file.
   * readme.txt describing group of files and project
   * intellegent comments throughout on how it was implemented.

 * Style 
   * Indentation
   * Variable names
   * Lucid prose

 * Debugging 
   * Compile time vs Run time errors.
   * Don't assume!
   * What to do when it doesn't work
      * Stare at the code (and the errors).
      * Add lots of print statements to see what it's really doing.
      * Remove (comment out) pieces until it works.
      * Ask for help.

 * On to perl specific syntax 

   * "nouns" (or data, or variables) have a funny character out front.
     Here's the complete list.

      $scalar   holds an integer, float, string, or reference

      @list     any (including non-uniform) collection of scalars
                also sometimes called an "array"

      %hash     a collection of paired ( key => value ) associations

      &code     one way to refer to a subroutine.
                (But usually the & can be omitted.)

   * Each sentence ends with ;

   * "verbs" (or function calls, or assignments) are things to be
     done to the nouns.  

   * "comments" start with # and go to the end of the line.

   * Assignment.
     "="  means "stick the thing on the right into the thing on the left."
     It does *NOT* claim equality or test for equality.  
     (Oops.  This syntax is usually confusing for beginning programmers.)

   * Example

   $x = 5.3;                 # Put the value 5.3 into variable $x.
   $answer = sqrt($x);       # Apply sqaure to 5.3, put result into $answer.
   print("The square root of 5.3 is $answer.\n");

 * Why does this language use "$x" rather than just "x"?
   * Name space clarity.  (More important than you might think.)
   * String interpolation.
   * Leaves more wriggle room in other aspects of syntax.
     (For example - parens after functions are optional.)

 * Note that even quotation marks "hi" are complicated verbs in Perl,
   with a lot going on behind the scenes.
   The quote has many variations, which we'll see in detail later.
   Here are a few examples to wet your whistle.

     $name = "Jim";                                 # define a scalar.
     print "My name is $name.\n";                   # interpolation
     print qq{My name is "$name".\n};               # same, another way.
     print 'My name is $name.\n';                   # no interpolation
     print q{"My name is "$name".\n};               # again, another way.
     print <<END;                                   # "here-is" string.
      My name is $name.
     END

 * Warnings and Strict

      #!/usr/bin/perl -w
      use strict;

   * Tells the compiler to catch some of your possible mistakes.

    Example: 

       $all = 5;
       print "The answer = $al1 \n";

    Try it with and without -w and strict.

 * Scope of variable names.

   * which means how long they exist and where they're valid.
   * Done with declarations  : "my" and "our"
   * In other languages the declaration is typically more detailed.
        * Those are called "strongly typed".
        * Perl isn't; it converts willy-nilly. 
          What does this do...
            $jimsLunch = "4 apples";
            $joesSnack = "5 oranges";
            print "For lunch we had ", $jimsLunch + $joesSnack, ".\n";

 * Enough; I'm rambling.

--------------------------------------------------------
 Jim Mahoney (mahoney@marlboro.edu)
 Intro Programming Fall 2003