Incrementing string - char letter for loop

You can do it with the ++ operator.

$i = 'aaz';
$i++;
print $i;
aba

However this implementation has some strange things:

for($i = 'a'; $i < 'z'; $i++) print "$i ";
This will print out letters from a to y.

for($i = 'a'; $i <= 'z'; $i++) print "$i ";
This will print out lettes from a to z and it continues with aa and ends with yz.