#! perl -slw use strict; my %subs = ( 100 => '50 50', 50 => '20 20 10', 20 => '10 10', 10 => '5 5', 5 => '2 2 1', 2 => '1 1', ); my $re_conversion = '(' . join( '|', sort{ length $b <=> length $a } keys %subs ) . ')'; my $input ); do { printf 'Denomination to change[100|50|20|10|5|2]: '; chomp( $input = ); } until exists $subs{ $input }; print $input while $input =~ s[$re_conversion][$subs{ $1 }]; __END__ [11:58:38.32] P:\test>406984 Denomination to change[100|50|20|10|5|2]: 20 10 10 5 5 10 2 2 1 5 10 1 1 2 1 5 10 1 1 1 1 1 5 10 1 1 1 1 1 2 2 1 10 1 1 1 1 1 1 1 2 1 10 1 1 1 1 1 1 1 1 1 1 10 1 1 1 1 1 1 1 1 1 1 5 5 1 1 1 1 1 1 1 1 1 1 2 2 1 5 1 1 1 1 1 1 1 1 1 1 1 1 2 1 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1