bug in php scripting?

I have recently been doing some php programming and have run into a problem with this code: <?php $char = "a"; do { echo $char++ . "<br/>"; } while ($char <= "z") ?> This code, as my colleagues and I have determined, should echo the value a, then break, then b, then break, then c, etc. However, when I execute the code I get a through z, aa through az, ba through bz, ca through cz, and so on and so forth until eventually getting to yz. Is there a problem with the code, or is it a problem with the php algorithm? Sorry if this is the wrong place to send this email. If so, can you redirect me to the correct person to contact? -Brett Jenson