: Undefined variable: pdo on line 22

  1  <header class="main-header">  
  2    <nav class="navbar navbar-static-top">
  3      <div class="container">
  4        <div class="navbar-header">
  5          <a href="index.php" class="navbar-brand">GENUINE COVID-19SITE</a>
  6          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar-collapse">
  7            
  8          </button>
  9        </div>
 10  
 11        <!-- Collect the nav links, forms, and other content for toggling -->
 12        <div class="collapse navbar-collapse pull-left" id="navbar-collapse">
 13          <ul class="nav navbar-nav">
 14            <li><a href="index.php">HOME</a></li>
 15            <li><a href="includes/about.php">ABOUT US</a></li>
 16            <li><a href="">CONTACT US</a></li>
 17            <li class="dropdown">
 18              <a href="#" class="dropdown-toggle" data-toggle="dropdown">CATEGORY <span class="caret"></span></a>
 19              <ul class="dropdown-menu" role="menu">
 20                <?php
 21               error gani io ?
 22                  $conn = $pdo->open();
 23                  try{
 24                    $stmt = $conn->prepare("SELECT * FROM category");
 25                    $stmt->execute();
 26                    foreach($stmt as $row){
 27                      echo "
 28                        <li><a href='category.php?category=".$row['cat_slug']."'>".$row['name']."</a></li>
 29                      ";                  
 30                    }
 31                  }
 32                  catch(PDOException $e){
 33                    echo "There is some problem in connection: " . $e->getMessage();
 34                  }
 35  
 36                  $pdo->close();
 37  
 38                ?>

while trying to add navigation bar on a page Notice