# exercise 3.1 by erikt(at)science.uva.nl

SOFTWARE

# read the first number
print "Please enter a number in characters: ";
$input = <STDIN>;
if (not defined $input) { $input = ""; }
chomp($input);

# process numbers while we have input
while ($input ne "") {

   # variant one: numbers with two parts separated by a hyphen 
   if ($input =~ /^(.*)-(.*)$/) {
      # store the two parts
      $decade = $1;
      $single = $2;
      # initialize the number at zero so we can add parts to it
      $number = 0;

      # there are only eight values to consider: 20,30,40,50,60,70,80,90
      if ($decade eq "twenty")     { $number += 20; }
      elsif ($decade eq "thirty")  { $number += 30; }
      elsif ($decade eq "forty")   { $number += 40; }
      elsif ($decade eq "fifty")   { $number += 50; }
      elsif ($decade eq "sixty")   { $number += 60; }
      elsif ($decade eq "seventy") { $number += 70; }
      elsif ($decade eq "eighty")  { $number += 80; }
      elsif ($decade eq "ninety")  { $number += 90; }
      # unknown word! make sure the number will be negative
      else { $number -= 1000; }

      # only nine values to consider: 1,2,3,4,5,6,7,8,9
      if ($single eq "one")      { $number += 1; }
      elsif ($single eq "two")   { $number += 2; }
      elsif ($single eq "three") { $number += 3; }
      elsif ($single eq "four")  { $number += 4; }
      elsif ($single eq "five")  { $number += 5; }
      elsif ($single eq "six")   { $number += 6; }
      elsif ($single eq "seven") { $number += 7; }
      elsif ($single eq "eight") { $number += 8; }
      elsif ($single eq "nine")  { $number += 9; }
      # unknown word! make sure the number will be negative
      else { $number -= 1000; }

   } else {
   # variant two: numbers consisting of a single part (no hyphen)
      # store the two parts
      $single = $input;
      # initialize the number at zero so we can add part to it
      $number = 0;

      # 28 values to consider: 0..20,30,40,50,60,70,80,90
      if ($single eq "zero")         { $number += 0; }
      elsif ($single eq "one")       { $number += 1; }
      elsif ($single eq "two")       { $number += 2; }
      elsif ($single eq "three")     { $number += 3; }
      elsif ($single eq "four")      { $number += 4; }
      elsif ($single eq "five")      { $number += 5; }
      elsif ($single eq "six")       { $number += 6; }
      elsif ($single eq "seven")     { $number += 7; }
      elsif ($single eq "eight")     { $number += 8; }
      elsif ($single eq "nine")      { $number += 9; }
      elsif ($single eq "ten")       { $number += 10; }
      elsif ($single eq "eleven")    { $number += 11; }
      elsif ($single eq "twelve")    { $number += 12; }
      elsif ($single eq "thirteen")  { $number += 13; }
      elsif ($single eq "fourteen")  { $number += 14; }
      elsif ($single eq "fifteen")   { $number += 15; }
      elsif ($single eq "sixteen")   { $number += 16; }
      elsif ($single eq "seventeen") { $number += 17; }
      elsif ($single eq "eighteen")  { $number += 18; }
      elsif ($single eq "nineteen")  { $number += 19; }
      elsif ($single eq "twenty")    { $number += 20; }
      elsif ($single eq "thirty")    { $number += 30; }
      elsif ($single eq "forty")     { $number += 40; }
      elsif ($single eq "fifty")     { $number += 50; }
      elsif ($single eq "sixty")     { $number += 60; }
      elsif ($single eq "seventy")   { $number += 70; }
      elsif ($single eq "eighty")    { $number += 80; }
      elsif ($single eq "ninety")    { $number += 90; }
      # unknown word! make sure the number will be negative
      else { $number -= 1000; }
   }

   # if $number < 0 then some error occurred
   if ($number < 0) { print "You have entered an unknown number: $input\n"; }
   else { print "You have entered: $number\n"; }

   # get the next number
   print "Please enter a number in characters: ";
   $input = <STDIN>;
   if (not defined $input) { $input = ""; }
   chomp($input);
}

# done
print "Thanks for using this program!\n";


TEST

erikt@stuwww:~$ perl -w 31.pl
Please enter a number in characters: one
You have entered: 1
Please enter a number in characters: twenty-three
You have entered: 23
Please enter a number in characters: drie miljoen
You have entered an unknown number: drie miljoen
Please enter a number in characters: seventy-seven
You have entered: 77
Please enter a number in characters: 
Thanks for using this program!