If you don't want to use sort, try this :

if (scalar(@numbers) > 0) {
  # compare only when array has entries
  my $highest = $numbers[0]; # set startvalue
  foreach my $compNum (@numbers){
    # compare all numbers in array
    $highest = $compNum if ($compNum > $highest);
  }
} else {
  # nothing to compare
}
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ps: code is not tested