The plugin generated 683 characters of unexpected output during activation

i am facing this error, please help me.

<?php
 /*Plugin Name: Contact Form
 Plugin URI: http://localhost/redspark/wp-admin
 Description: Contact Form Create & Retrive By Ajax
 Author: Shifa Memon
 Author URI: http://localhost/redspark/wp-admin
 Version: 1.0 */
 function custom_contact_form_create(){
// echo "Active";
// die();
global $wpdb;
global $table_prefix;
$table = $table_prefix . 'contact_us';
    $sql = "CREATE TABLE 'wp_contact_us' (
      `id` int(50) NOT NULL PRIMARY KEY AUTO_INCREMENT,
      `name` varchar(50) NOT NULL,
      `email` varchar(100) NOT NULL,
      `subject` text NOT NULL,
      `message` longtext NOT NULL,
      `timestamp` timestamp NOT NULL DEFAULT current_timestamp() ON 
       UPDATE current_timestamp())";
       $wpdb->query($sql);
}
register_activation_hook(__FILE__,'custom_contact_form_create');

function custom_contact_form_delete(){
   global $wpdb;
   global $table_prefix;
   $table = $table_prefix.'contact-us';
   $sql = "DROP TABLE $table";
   $wpdb->query($sql);
   // echo "Deactivate";
  }
  register_deactivation_hook(__FILE__ ,'custom_contact_form_delete');

    ?>

The Solutions:

Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.

Method 1

finally plugin is activated…

this is code…

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0