my @nums = qw /3.34 3.67 4.75 4.98/;
    my $diff = -1;

    for (my $i = 1; $i < @nums; $i ++) {
        my $d = abs ($nums [$i] - $nums [$i - 1]);
        $diff = $d if $diff < $d;
    }

    print "Greatest difference is $diff\n" unless $diff < 0;