C F G G7

##</code><code>##

    C# F# G# G#7

##</code><code>##

use strict;
use warnings;

my %notes_hash = (
    'A'  => 0,
    'A#' => 1,
    'B'  => 2,
    'C'  => 3,
    'C#' => 4,
    'D'  => 5,
    'D#' => 6,
    'E'  => 7,
    'F'  => 8,
    'F#' => 9,
    'G'  => 10,
    'G#' => 11
);

my @notes_array = ( sort( keys(%notes_hash) ) );

sub transpose {
    my ( $note,      $amount )    = @_;
    my ( $base_note, $modifiers ) = $note =~ m/^([ABCDEFG]#?)(.*)/;
    return 
    $notes_array[ ( ( $notes_hash{$base_note} + $amount ) % 12 ) ]
      . $modifiers;
}

print transpose( 'C#7', 1 );