[PHP] Letter incrementing

[Brent Clark]

Hi all

Does anyone know how, or even if it is possible to increment a letter from the 
alphabet.

I know that if you use 
e.g

$o = 1;
$o++;

will result in $o ==  2,.

But I need to do a $variable = "B";
and then do a $variable++ that will result in
$variable == "C"

Kind Regards
Brent Clark