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

print "\nMean Average Program\n\nenter values, when done enter 'done':";

my @value;

while (my $input=<>){
  chomp $input;
  last if uc($input) eq "DONE";
  #Validate that the input is only digits-should reallly [use Scalar::Util qw(looks_like_number)]
  print ("INVALID value '$input' -ignored\nTry again:") , next
        unless $input =~ /^[+-]?\d+(\.\d+)?$/; # Crude floating-point test
  push @value, $input ;
  print "Enter a value('done' if finished): ";
}

my $mean = 0;
for my $val (@value){
  $mean += $val;
}
if (scalar @value){ # There is at least one @value - avoid div by 0
   $mean = $mean / scalar(@value);
}

print "\nThe mean of your values is $mean\n";