I've tried a trick I often use in C++; the PHP syntax should be identical:

$a=0;
while ([condition]) {
  $mystring= ++$a%=8 ? "A" : "B";
  [...]
}

the value of $mystring should be "B" seven times and then "A" once, keeping the value of $a in the range [0..7].

If $a is useless for other purposes, the following gives the same result:

$a=0;
while ([condition]) {
  $mystring= ++$a%8 ? "A" : "B";
  [...]
}

whith two differences:
$a is no loger necessarily in the range [0..7] and, above all, tha latter works, but tha former doesn't!

I've tried to parse "++$a" writing
  $mystring= (++$a)%=8 ? "A" : "B";

but it doesn't work.

Since this problem is related to operators, I don't think you need information about my modules or my system, but if I'm wrong ask me for that.
Thank you.

Regards,

Davide Spagnoli