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

print "Mean Average Program\n";

my @values;

push @values, $_ while (defined ($_ = nextValue ()));

my $sum;
$sum += $_ for @values;
my $mean = $sum / @values;

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


sub nextValue {
    print "Enter a value ('done' if finished): ";

    while (1) {
        chomp (my $value = <>);
        return if $value =~ m'done'i;
        return $value if $value =~ /[+-]?\d+(\.\d*)?([+-]?[eE]\d+)?/;

        print "I don't recognise $value as a number or as 'done'. Try again: ";
    }
}

##</code><code>##

Mean Average Program
Enter a value ('done' if finished): 2
Enter a value ('done' if finished): 2
Enter a value ('done' if finished): 3
Enter a value ('done' if finished): done

The mean of your values is 2.33333333333333