incrementing not as expected

Hi guys, This is NOT possible (note: $a remains as a string) : for ($a = 'a'; $a <= 'z'; $a++) { $foo[] = $a; } Yet this does work nicely : $l = 'a'; for ($a = 1; $a <= 26; $a++) { $foo[] = $l++; } I'd like to know why exactly this is the case. The first route goes from : 'a' to 'yz' , 675 values! I suspect the issue is $string <= 'string' but i don't appreciate types enough to know why exactly, just guesses. I've even gone crazy and tried this too : for ((string) $z = 'a'; (string) $z <= 'z'; (string) $z++) { (string) $foo .= (string) $z; } Curiously confused, Philip -- Disclaimers : My code may not be perfectly efficient but it gets the job done. It's called : "Learn through experience."