为rand函数加入随机数种子

list($usec, $sec) = explode(" ", microtime());
srand((int)($usec*10));
$rand_value = rand(0, 99);
echo($rand_value."<br>");
$rand_value = rand(0, 99);
echo($rand_value."<br>");
$rand_value = rand(0, 99);
echo($rand_value."<br>");