foreach 输出遇到的问题，求各位老师解决
$citycode = array("北京"=>"101010100","海淀"=>"101010200","朝阳"=>"101010300");
foreach ($citycode as $arr) {
echo $arr.'\\n';
}
saveFile('file.txt',$arr);
我希望file.txt里的内容为：
101010100,101010200,101010300
这个$arr要怎么写？
------解决思路----------------------
<br /><?php<br /><br />$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 />
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