Untitled

<?php
$servername = "localhost";
$dbname = "databasename";
$username = "username";
$password = "password";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected successfully :D";
    }
catch(PDOException $e)
    {
    echo "Connection failed: " . $e->getMessage();
    }
?>

<!DOCTYPE html>
<html>
<head>
 <?php require 'db.php';
 $conn;
 $add1sql = "UPDATE supplies SET quantity = quantity + 1 WHERE Id=1";
?>
    <title>Homepage</title>
    <link rel="stylesheet" type="text/css" href="style/main.css">
</head>
<body>
    <h1>testpage</h1>
    <form method="POST" action="<?php exec($add1sql) ?>">
        <input type="submit" name="+1" value="+1"/>
    </form>

</body>
</html>