Merhaba, dosyayı şu şekilde güncelleyiniz;
<?php include("fonksiyon.php");  ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" href="dosya/boost.css" >
<title>PDO ÜYELİK SİSTEMİ</title>
</head>
<body>
 
<div class="container-fluid">
   <div class="row">
    
      <div class="col-md-6 mx-auto mt-4" >
        
           <?php
         $hareket=$_GET["hareket"];
            
         switch($hareket):
            case"ekle":
            break;
            
            case"uyeguncelle":
            break;
            
            case"uyesil":
            break;
             default:
         ?>
        
        
         <table class="table table-bordered table-striped text-center bg-white">
            <thead>
            <tr>
            <th colspan="6"> <a href="index.php?hareket=ekle" class="btn btn-success"> Üye Ekle  </a></th>
                      
            </tr>
            </thead>
         <thead>
            <tr>
            <th class="font-weight-bold">AD</th>
            <th class="font-weight-bold">SOYAD</th>
            <th class="font-weight-bold">YAŞ</th>
            <th class="font-weight-bold">AİDAT</th>
            <th class="font-weight-bold">GÜNCELLE</th>
            <th class="font-weight-bold">SİL</th>            
            </tr>
            </thead>
            <tbody>
            
            <?php
         $clas= new uye;
        
          
            echo $clas->listele($baglanti);        
          
            
         ?>
          
          
            </tbody>
        
            </table>
            <?php
         break;
          endswitch;        
          
            
         ?>
          
          
        
        </div>
    
    
    </div>
 
  
 
</div>
 
</body>
</html>