如何根据php中前一个输入的值限制在文本框中输入的值

I have 2 textboxes one is for maximum marks and the other for the obtained marks.. The value to be entered in the second box must be restricted in such a way that it is less than or equal to the maximum marks.. Only numbers must be entered into those boxes..

Maximum Marks<input type=text name=maxmarks maxlength='2' >
Obtained marks<input type='text' maxlength='2' name='obtmarks'>

Please help me with this.. Thank you in advance..

Well if you want to do it client side, you will have to use Javascript. If you want to do it server-side, why don't you send them back the page with an error message if the second number exceeds the first. You might also might want to look into HTML5 input options if that is an available option for you. Those will automatically do the number validation.

You could try something like this...

   $response_array = array();

   if($obtained > $max){
       $response_array['status'] = 'error';
       $response_array['message'] = '<div class="alert alert-error">Obtained to big</div>';

   }
   if(!is_numeric($obtained){
       $response_array['status'] = 'error';
       $response_array['message'] = '<div class="alert alert-error">Obtained not a number</div>';
   }
   echo json_encode($response_array);

This is pseudo code, obviously you will need to tweak it for your purpose.

First you have to make checks in your php script that you submit the form, you can use javascript after to make it more user friendly but if someone change the source code or just turn javascript off he will be able to submit anyting. In your process_form.php:

    session_start();
    $errors = array();
    if (!isset($_POST['maxmarks']) || empty($_POST['maxmarks'])) {
         $errors[] = 'The Maximum Marks field is required.';
    }
    else {
        if (!is_int($_POST['maxmarks'])) {
            $errors[] = 'The Maximum Marks field must be an integer.';
        }
        else {
           $maxmarks= (int) trim($_POST['maxmarks']);
        }
    }

    if (!isset($_POST['obtmarks']) || empty($_POST['obtmarks'])) {
         $errors[] = 'The Obtained Marks field is required.';
    }
    else {
        if (!is_int($_POST['obtmarks'])) {
            $errors[] = 'The Obtained Marks field must be an integer.';
        }
        else {
           $obtmarks= (int) trim($_POST['obtmarks']);
        }
    }

    if (!empty($errors)) {
        $_SESSION['form_errors'] = $errors;
        header('Location: your_form.php');
        die();
    }
    else if ($obtmarks > $maxmarks){
        $errors[] = 'The Obtained Marks must be less or equal to Maximum Marks.';
        $_SESSION['form_errors'] = $errors;
        header('Location: your_form.php');
        die();
    }
    else {
        //process data
    }

In your_form.php now:

   session_start();
   if (isset($_SESSION['form_errors']) && !empty($_SESSION['form_errors'])) {
       $errors = $_SESSION['form_errors'];
       unset($_SESSION['form_errors']);
   }

   echo '<ul>';
   if (isset($errors)) {
       foreach($errors as $error) {
           echo '<li>' . $error . '</li>';
       }
   }
   echo '</ul>';
   //your form here