#!/usr/bin/perl
use strict;
use warnings;

my ($lower, $upper) = (40, 100);

for my $num (17,42,99,111) {

    my $is_between = (sort {$a <=> $b} $lower, $upper, $num)[1] == $num;
    
    printf "$num is%s between $lower and $upper\n", $is_between ? "" : " not";
}

__END__
17 is not between 40 and 100
42 is between 40 and 100
99 is between 40 and 100
111 is not between 40 and 100