c = c.charCodeAt(0);
c++;
c = c.toString();
temp = c;
c = String.fromCharCode(temp);
line += c;

##</code><code>##

line += String.fromCharCode(c.charCodeAt(0)+1);

##</code><code>##

$line .= chr(ord($c)+1);

##</code><code>##

use strict;
use warnings;
my $line = "hello";
my $c = "A";
print "1. line='$line' c='$c'\n";
$line .= chr(ord($c)+1);
print "2. line='$line' c='$c'\n";

##</code><code>##

1. line='hello' c='A'
2. line='helloB' c='A'