my $highest = 0;
my $lowest = 1_000_000_000;
foreach (@list_of_int) {
   $highest = $_ if $_ > $highest;
   $lowest = $_ if $_ < $lowest; # was $highest - see update
}

##</code><code>##

my $highest = 0;
my $lowest; # undef
foreach (@list_of_int) {
   $highest =>> $_;
   $lowest =<< $_;
}

##</code><code>##

my $highest = '';
my $lowest; # undef
foreach (@list_of_string) {
   $highest eg $_;
   $lowest el $_;
}