如何在php中为输入框设置负值

<input type="number" class="addme" value="'.$_REQUEST['pbill'].'" name="amount" min="0" required="required" placeholder="Enter amount of Pending Bills" title="Enter amount of Pending Bills" pattern="[0-9]{1,}" />

How do I ensure that the value to be input in the above will be a negative value?

after wide consultations i have come to the conclusion that this is the most viable answer...thanks to all that helped in the query $_REQUEST['amount'] = -$_REQUEST['amount'];

There is nothing sure about using pattern. You should check it out server side. But if You would like to use pattern to check this out, the pattern should be \-[0-9]+

As for PHP:

You simply check the value before inserting it to database:

if($_REQUEST['amount'] >= 0){ // $_REQUEST is generally for $_GET and $_POST
    echo "Incorrect amount given. Please try again.";
    die();
}

check the posted value, like

 $amount = $_POST['amount'];

 if($amount > 0) {
      //echo 'positive';
      $req_amt = (0 - $amount);
 } else {
      echo 'negative or 0';
 }