PHP Tutorial: Generate random password that includes numbers and letters

The following code illustrates an excellent password generator.

<?php
echo password_gen(6,6);
function password_gen($min=6,$max=6){ /*has a default min value of 6
and maximum value of 6*/
$pwd=""; // to store generated password
for($i=0;$i<rand($min,$max);$i++){
  $num=rand(48,122);
  if(($num >= 97 && $num <= 122))     $pwd.=chr($num);
  else if(($num >= 65 && $num <= 90))  $pwd.=chr($num);
  else if(($num >=48 && $num <= 57))    $pwd.=chr($num);
  else    $i--;
}
return $pwd;
}
?>