验证码字符串没有输出？？？？求解
function buildRandomString($type){
if($type==1){
$chars=join("", range(0, 9));
}elseif(type==2){
$chars=join("", array_merge(range("a", "z"), range("A", "Z")));
}elseif(type==3){
$chars=join("", array_merge(range(0, 9), range("a", "z"), range("A", "Z")));
}
echo $chars;
}
buildRandomString(2);
type=2和3时没有输出，等于1时正常。使用的IE和Firefox浏览器
