一个循环判断入入了误区请求指导

$str ="3,8,9,10,11,";
$array = explode(",", $str);
foreach($array AS $_key=>$value){ 
 $show.="$value";
}
if($show==3){
		echo "你好";
}elseif($show==11){
	echo "我好";	
}else{
		echo "都好";
}

$str ="3,8,9,10,11,";
$array = explode(",", $str);
foreach($array AS $_key=>$value){ 
  if($value==3){
     echo "你好";
  }elseif($value==11){
     echo "我好";   
  }else{
    echo "都好";
  }
}

echo '';

$str ="3,8,9,10,11,";
$array = explode(",", $str);
foreach($array AS $_key=>$value){ 
    echo show($value);
}

function show($v){
    if($v==3){
        return '你好 ';
    }elseif($v==11){
        return '我好 ';
    }else{
        return '都好 ';
    }
}
?>