sub print_sub_menu
{
   my %sub_menu = %{(shift)};
   my $i = 1;
   my $index = $i; #index of the hash
   #get every item of the input-hash
   #needs $index for cases, where not every number has a corresponding value
   for ($i; $i < keys(%sub_menu); $i++)
   {
      while (! exists $sub_menu{$index})
         { $index++; }
      print "\t$index - $sub_menu{$index}\n";
      $index++;
   } #<-- beanstandete Zeile
   return 0;
}