#!/usr/bin/perl -w
################  List Function Demo  ##################
@list = (1,"hello","3","goodbye");
print "List is: @list\n";
print "Highest index of list is: $#list\n";
print "Number of elements in list is: ",scalar(@list),"\n";

print "Last element of list is: ", pop(@list),"\n";
print "First element of list is: ", shift(@list),"\n";

unshift(@list,1,2);
print "List is: @list\n";
push(@list,4,5);
print "List is: @list\n";

#####  Proof that negative indices start at list end!
@list = ("hello", "goodbye", "hola", "aloha", "sayonara");
print "$list[-1] $list[-2]\n";  #####  List elements are SCALARS!!!! 

foreach $element (@list)   ######  The correct way to print lists!!
{
     print $element;
     $element =~ s/a/X/g;  ######  Changes the list elements!!
}
print "@list\n";    ######  Observe the changed list!!

###############  Hash Manipulation Demo  #####################

%music = ("Fur Elise" => "Beethoven",
"Art of the Fugue" => "Bach",
"Sonata for Two Pianos and Percussion" => "Bartok");

foreach $key (sort(keys(%music)))
{
    print "$key\n";
}

foreach $value (values(%music)) { print "$value\n" }  ##### Acceptable format!

print "Yippee\n" if (exists($music{'FUR ELISE'}));
print "Hooray\n" if (exists($music{'Fur Elise'}));

print "$piece: $composer\n" while ($piece,$composer) = each(%music);

delete $music{"Fur Elise"};     ######  Removes Key/Value Pair!!
print "$piece: $composer\n" while ($piece,$composer) = each(%music);
#########################  Output Below  ########################

List is: 1 hello 3 goodbye

Highest index of list is: 3
Number of elements in list is: 4

Last element of list is: goodbye
First element of list is: 1
List is: 1 2 hello 3
List is: 1 2 hello 3 4 5

sayonara aloha  #####  $list[-1] and $list[-2]
hello     #####  List elements before substitution.
goodbye
hola
aloha
sayonara

hello goodbye holX XlohX sXyonXrX   #####  List elements AFTER substitution

Art of the Fugue     ######  Listing of sorted keys.
Fur Elise
Sonata for Two Pianos and Percussion

Bach      #####  Values of the hash -- notice lack of sorted order!!
Bartok
Beethoven

Hooray    #####  Proof that an "exists" is true only if key is an EXACT match.

Art of the Fugue: Bach     ######  Dump of hash using "each" function! 
Sonata for Two Pianos and Percussion: Bartok
Fur Elise: Beethoven

Art of the Fugue: Bach     ######  Fur Elise/Beethoven deleted in this listing! 
Sonata for Two Pianos and Percussion: Bartok

################  Summary of Relevant List/Hash Concepts  ##################

1) Shift removes the leftmost (index 0) element of a list and returns the
   shifted-off value.

2) Unshift places one or more elements onto the leftmost part of a list.

3) Pop removes the rightmost (highest index) element of a list and returns
   the popped-off value.

4) Push places one or more elements onto the rightmost part of a list.

5) Use push or unshift to put new elements in a list, not:

       @list = (@list, $stuff, $junk);
                  or
       $list[$i] = $whatever;    ####  Avoid indices unless necessary!! 

   Unless you have a specific need for a list index variable (like $i), use
   push or unshift.  This speeds the programs performance and also means you
   have one less variable to keep track of.

6) When using a function which returns a list of known size, collect
   the elements like:

      ($name, $salary, $department) = function_returning_list();
                         and NOT 
      @person_data = function_returning_list()

   It's much easier to tell what $name means than @person_data[0].
   Remember this when using functions like split that return lists!!