Thomas H. George wrote:
I am inching my way through INTERMEDIATE PERL and tried using hashes to
solve Chapter 4, Problem 2. I never used hashes before but my attempted
solution convinced me of their value as contrasted to the solution with
arrays.
The Problem: My solution works but with an error I can't eliminate.
The difficulty is in the next to last line, the 'unless ...' statement
which causes warning:
Use of uninitialized value in string eq at chap4-take6.pl line 49.
Here is the complete program:
#!/usr/bin/perl -w
#
use strict;
my %required_list = (
life_jacket => 'preserver',
lotion => 'sunscreen',
water => 'water_bottle',
coat => 'jacket',
);
my %captain = (
name => 'skipper',
life_jacket => 'preserver',
lotion => 'sunscreen',
water => 'water_bottle',
shirt => 'blue_shirt',
coat => 'jacket',
hat => 'cap',
);
my %mate = (
name => 'gilligan',
shirt => 'red_shirt',
hat => 'cap',
socks => 'lucky_socks',
water => 'water_bottle',
);
my %passenger = (
name => 'professor',
lotion => 'sunscreen',
water => 'water_bottle',
calculator => 'slide_rule',
power_supply => 'batteries',
entertainment => 'radio',
);
my @crew = (\%captain, \%mate, \%passenger);
check_required_items (@crew);
sub check_required_items {
You are using a subroutine and passing a list to it but you never use
that list inside the subroutine. In fact, you are accessing the array
@crew and the hash %required_list from outside the subroutine, so is
there any good reason to use a subroutine at all?
foreach my $person (@crew) {
my $who = ${$person} {'name'};
That is usually written as:
my $who = $person->{ name };
my @keys = keys %required_list;
foreach (@keys) {
unless ($required_list {"$_"} eq ${$person} {"$_"}) {
You don't need to quote scalar variables:
perldoc -q quoting
Instead of comparing every %required_list key to %$person using 'eq' you
should use exists() to check for the existence of those keys.
perldoc -f exists
And, ${$person} {"$_"} is usually written as $person->{ $_ }
print "$who is missing $_\n";
}
}
}
}
So you want something like:
my @crew = \( %captain, %mate, %passenger );
check_required_items( \%required_list, @crew );
sub check_required_items {
my ( $req_list, @crew ) = @_;
for my $person ( @crew ) {
for my $required ( keys %$req_list ) {
unless ( exists $person->{ $required } ) {
print "$person->{ name } is missing $required\n";
}
}
}
}
John
--
Those people who think they know everything are a great
annoyance to those of us who do. -- Isaac Asimov
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