#!/usr/bin/perl


=pod

=head1 Associative Arrays and Hashes in a script with functions (called subs)


Note: The above line starts interpreter languages such as perl and shell

Now that you have seen scalars and arrays in action, I will introduce you to
hashes, sometimes known as associative arrays.

=head1  Perldoc

The odd marks above (=head1) are the perldoc format.
Type "perldoc <perlscipt>" and the comments will get formatted using this syntax

=cut

%my_hash = ( 'a', 1, 'b', 2, 'c', 3, 'd' , 0, 'e', 0) ;

# Here the keys are a, b, d and d and the values are 1 2 3 1
# The letters should have single or double quotes around them.  
# A double quote allows variables to show their contents, 
# a single quote will print the string including the '$'.
# A backtic actually sends a call out to the system and will fill up
# an array with the lines returned by the call. The next script shows that.
# The operator "keys" is used below:

@keys_arr = keys %my_hash ;

# I will also introduce you to the "if", "elsif" and "else" operators 
  
$last_value = 0 ;

foreach $key (@keys_arr) {

   $value = $my_hash{ $key } ;

   print "key: ".$key.", value: ".$value."\n" ;

   if ( $value > $last_value ) { 
      print "this value is greater than the prevous value in the hash\n" 
   }
   elsif ( $value == $last_value ) { 
      print "this value EQUALS the last\n"
   }
   else { 
      print "this value is NOT greater than the last\n"
   }

   $last_value = $value 
}

=head1 Comments on blocks 

This "if/else" statement has two statement blocks in it, each surrounded by 
curly braces.  Since a semicolon ends a statement, one placed after the "if" 
statement would have isolated the "else" statement from it, causing a "compile"
error.

Also, you dont have to use a semicolon on the last or only line in a block or 
the last line in a script.

Just to round things out, I want to show you how a function (sub for subroutine
) works.

=cut


sub key_val_demo {
    my @arr = @_    ; # "@_" is the array "in play" and I fill the array 
                      # "@arr" with its contents.
                      # "my" is very important because it keeps values within
                      # the scope of a curly braced block, in this case a sub. 

    my %hash = @arr ; # As I said, perl has nice tricks, you can convert an
                      # array into a hash this simply, but the array has to be
                      # formatted in key value pairs  

    my @keys = keys %hash ; my @vals = values %hash ;
                      # keys and values are built in functions 
    my $keys_string = join (' ', @keys ) ;
    my $vals_string = join (' ', @vals ) ;
    my $out_string = "From the sub:\n"   ;
    $out_string .= "\n keys: $keys_string \n values: $vals_string\n" ;
       # the "\n" is perl for a newline and the ".=" joins the contents of 
       # the "$out_string" with the string after it
    return $out_string ;
       # this sends the string back out without printing it, 
       # you will see how it works in a moment 
       
}

$print_out = &key_val_demo( 'a', 1, 'b', 2 , 'c', 3) ;
       # I could have set the a, 1, b, 2... arguments to be an array or even 
       # hash,  &keys(@arr), or &keys(%hash), perl is very flexible
       # If a sub is called after it is declared in script the "&" can
       # be elminated

print $print_out ;
       #this is what was returned from the function, errr, sub.

=head1 End Comments

The vast majority of scripts out there are no more complicated than this 
because perl is primarily a systems language which grew up along with the rest 
of the computing world.  Part of our philosophy is that "what works for you, 
works for us."  
 
We truly hope you like the style of programming and are eager for the object 
oriented stuff in the next example. 

=cut

  #Copyright CXN, Inc., 2000, please email john@thinman.com for copy permission