Convert a decimal number to its literal expression in English

num2english.pl

#! /usr/local/bin/perl -w

# Convert a decimal number to its literal expression in English.

use strict;
use warnings;
use Getopt::Std;

my %opts;
getopts("u", \%opts);

my @units = ( "zero", "one", "two", "three", "four",
	      "five", "six", "seven", "eight", "nine" );
my @teens = ( "ten", "eleven", "twelve", "thirteen", "fourteen",
	      "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" );
my @tens = ( "", "ten", "twenty", "thirty", "forty",
	     "fifty", "sixty", "seventy", "eighty", "ninety" );

sub name100 {
    use integer;
    my $n = shift;
    die "Bad input to name100" unless $n >= 0 && $n < 100 && $n == ($n/10)*10+($n%10);
    if ( $n < 10 ) {
	return $units[$n];
    } elsif ( $n < 20 ) {
	return $teens[$n%10];
    } else {
	my $s = $tens[$n/10];
	$s .= "-".$units[$n%10];
	return $s;
    }
}

sub name1000 {
    use integer;
    my $n = shift;
    die "Bad input to name1000" unless $n >= 0 && $n < 1000 && $n == ($n/100)*100+($n%100);
    if ( $n < 100 ) {
	return name100($n);
    } else {
	my $s = $units[$n/100] . " hundred";
	if ( $n%100 == 0 ) {
	} else {
	    $s .= ($opts{u}?" ":" and ").name100($n%100);
	}
	return $s;
    }
}

sub namemillion {
    use integer;
    my $n = shift;
    die "Bad input to namemillion" unless $n >= 0 && $n < 1000000 && $n == ($n/1000)*1000+($n%1000);
    if ( $n < 1000 ) {
	return name1000($n);
    } else {
	my $s = name1000($n/1000) . " thousand";
	my $t = name1000($n%1000);
	$t = "and ".$t unless $t =~ /\band\b/ || $opts{u};
	$s .= " ".$t if $n%1000;
	return $s;
    }
}

sub namebillion {
    use integer;
    my $n = shift;
    die "Bad input to namebillion" unless $n >= 0 && $n < 1000000000 && $n == ($n/1000000)*1000000+($n%1000000);
    if ( $n < 1000000 ) {
	return namemillion($n);
    } else {
	my $s = name1000($n/1000000) . " million";
	my $t = namemillion($n%1000000);
	$t = "and ".$t unless $t =~ /\band\b/ || $opts{u};
	$s .= " ".$t if $n%1000000;
	return $s;
    }
}

binmode STDOUT, ":utf8";
while ( <> ) {
    chop;
    printf "%s\n", namebillion($_);
}