Hi monks, I am studying the references on perlreftul. It showed an example of using references to a hash containing countries and cities(http://perldoc.perl.org/perlreftut.html). I created a test file containing the country city list, 
    Chicago, USA
    Frankfurt, Germany
    Berlin, Germany
    Washington, USA
    Helsinki, Finland
    New York, USA

[download]
then test the code as below: 
#!/usr/bin/perl -w
use strict;
my %table;
while (<>){
    chomp;
    my ($city,$country)=split/,/;
    $table{$country}=[] unless exists $table{$country};
    push @{$table{$country}}, $city;
    
}
my $a=$table{"USA"};
print $a;  #line 12


foreach my $country (sort keys %table){
    
    if ($country eq "USA"){
    
    print "USA is found\n";
    }
    else{}
}

[download]
Wierd thing happend. first, I can not print the element of $table{"USA"}, giving the error "Use of uninitialized value in print at country_city.pl line 12, <> line 6.". Second, the foreach loop can not find $country equals to "USA", thus, it can not print "USA is found", it just printed nothing. What happened? This really confused me. Thanks.

In reply to Can not print hash element by lightoverhead

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