<?php
         if($_SERVER["REQUEST_METHOD"]=="POST"){
              $id=$_POST["stdid"];
              $id=trim($id);
              $id=stripcslashes($id);
              $id=htmlspecialchars($id);!

          $host='localhost';
          $user='root';
          $pass=null;
          $db='libman';
          $con=mysqli_connect($host,$user,$pass,$db)or die ("unable to connect");

         $query="select * from management where id='$id'";
        $check=duplicate($query);
         if($check!=0){
             $sqlinsert="insert into management(id) values ('$id')";
             mysqli_query($con,$sqlinsert);


         }else{

            $del="delete from management where id='$id'";
             mysqli_query($con,$del);


         }

         $sqlsearch="select * from management";
         $checker=mysqli_query($con,$sqlsearch);
         $rowcount=mysqli_num_rows($checker);
         $seat=200-$rowcount;
         echo $seat;
         echo "<br>";
         while($show=mysqli_fetch_array($checker)){

            echo $show["id"];
            echo "<br>";

            }
         }
        function duplicate($query){
             global $con,$flag;
            if(mysqli_query($con,$query)){

                $res=mysqli_query($con,$query);
                return $res;

            }
            if(empty(mysqli_query($con,$query))){
              $res=mysqli_query($con,$query);
                return $res;
            }
        }

?>