#!/usr/bin/perl -w
use strict;

my $total = 0;
my $nums  = 0;

print "Average numbers: enter numbers then \"done\"\n";

while ( (print "Enter Number: "), 
        (my $line=<STDIN>) !~ /^\s*d(?:one)?\s*$/i  
      )
{
   next if $line =~ /^\s*$/;  #re-prompt on blank lines

   if ($line !~ /^\s*((-?\d*)(\.\d*)?)\s*$/) #valid float
   {
       chomp($line); 
       print "$line is not a valid number! Try again!\n";
       next;
   } 
   $total += $1;  
   $nums++;
}

print "average is : ",$total/$nums,"\n";