use strict;

my $list        = { head=>undef, tail=>undef };

while (1)
{
    print '<i>nput, <o>utput : ';
    chomp (my $input = <STDIN>);
    
    if ($input eq  'i')
    {
        add($list);
        next;
    }        

    if ($input eq 'o')
    {
        show($list);
        next;
    }
}

sub add
{
    my ($list) = @_;
    chomp (my $input = <STDIN>);

    my $newnode = [undef, $input];
    $list{tail}[0]= $newnode;
    $list{tail}= $newnode;
}