if $number is a key in the hash, print its value, end of the history

else you need to reduce the problem 

     while $number is not undef
      extract the last number of the chain with pop
      if the popped number = 0 forget this number
      else my $units = this number

      pop again 
      if you have a zero: good bye zero!
      else my $teen = this number *10

      pop again
      if you have a zero: good bye zero!
      else my $hundred = this number
      my $thereis_a_hundred = true;

      ... etc, etc ...

      pop again ...  oups, nothing left to pop, we obtain undef and exit the loop,
      my $googolplex = ''; # this variable was not reached, its value is still the null string, so if you print it nothing occurs
      }

##   print all variables you have collected in reversed position and add some extra strings
    
## first whe prepare the extra chains, this could be done before also

if ($there_is_hundred is true){my $hundred_str = "hundred and "}
  else {$hundred_str = ''};
if ($there_is_thousand is true){my $thousand_string =  " thousand, "}
  else {$thousand_string = ''};

# ... etc

# we finish

  print .......  %number[$thousand] $thousand_string %number[$hundred] $hundred_str %number[$teen], %number[$unit];

# and we close all with the required "}"