PHP在内部循环排序

I want to sort stuff while looping

$arr = array('c','a''b');
 foreach($arr as $alpha){
  sort($alpha);
  echo $alpha."-";
 }

and it should end up with a-b-c
how to get it done ?

$arr = array('c','a', 'b');
sort($arr);
foreach($arr as $alpha) {
    echo $alpha . "-";
}

Sort only needs to be called once.