PHP code to generate random numbers or strings_PHP tutorial

/**
* Generate a random string
*
* Generate a random string of specified length and return it to the user
*
* @access public
* @param int $len generate Number of digits in string
* @return string
*/
function randstr($len=6) {
$chars='ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz0123456789-@#~';
// characters to build the password from
mt_srand((double)microtime() *1000000*getmypid());
// seed the random number generator (must be done)
$password='';
while(strlen($password)<$len)
$password.=substr($chars,(mt_rand()%strlen($chars)),1);
return $password;
}