PHP foreach给出错误“未定义的变量”[重复]

I'm making my project with foreach.. This works on my old webhosting while in my new hosting it doesn't work..

It gives an error:

PHP Notice:  Undefined variable: generate_me

I don't know what is wrong in my code. Any body help?

$first = true;
foreach ($_POST as $key=>$value) {
$$key = $value;
    if ( $first ){
        $generate_me .= "?".$key."=".rawurlencode($$key);
        $first = false;
    }
    else{
        $generate_me .= "&".$key."=".rawurlencode($$key);
    }
}

</div>

$generate_me = ''; // add this line and it should work with no error
$first = true;
foreach ($_POST as $key=>$value) {
$$key = $value;
    if ( $first ){
        $generate_me .= "?".$key."=".rawurlencode($$key);
        $first = false;
    }
    else{
        $generate_me .= "&".$key."=".rawurlencode($$key);
    }
}