#!/usr/bin/perl
# Fig. 4.18: fig04_18.pl
# Demonstrating functions delete, exists and defined.

%hash = ( Karl  => 12,
          Joe   => 43,
          Shawn => 0,
          Paul  => 11, 
          Bill  => undef );

# obtain the list of hashKeys and display each key-value pair
@hashKeys = keys( %hash );

for ( $i = 0; $i < @hashKeys; ++$i ) {
   print "$hashKeys[ $i ] => $hash{ $hashKeys[ $i ] }\n";
}

# delete the element with key 'Joe' from %hash
delete( $hash{ 'Joe' } );

# this loop determines if each key exists, is defined and
# whether the value for the key evaluates to true or false
while ( $key = pop( @hashKeys ) ) {
   print "\n";

   # determine if a particular key exists 
   if ( exists( $hash{ $key } ) ) {
      print "$key exists in the hash.\n";
   }
   else {
      print "$key doesn't exist in the hash.\n";
   }

   # determine if the value for the key is defined
   if ( defined( $hash{ $key } ) ) {
      print "$key is defined as $hash{ $key }.\n";
   }
   else {
      print "$key is undefined.\n";
   }

   # determine if the value for the key is true or false
   if ( $hash{ $key } ) {
      print "$key is true.\n";
   }
   else {
      print "$key is false.\n";
   }
}


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