foreach 输出遇到的有关问题，求各位老师解决

<br /><?php<br /><br />$citycode = array("北京"=>"101010100","海淀"=>"101010200","朝阳"=>"101010300");<br /><br />foreach ($citycode as $arr => $value) {<br />    $citycode[$arr] .= ',';<br />}<br />// saveFile('file.txt',$arr);<br />file_put_contents('file.txt', $citycode);<br /><br />?><br />

$arr = implode(',', $citycode);<br />saveFile('file.txt',$arr);

<br />$citycode = array("北京"=>"101010100","海淀"=>"101010200","朝阳"=>"101010300");<br />saveFile('file.txt',implode(',',$citycode));<br />