code

<?php
require_once 'register.php';

function check_email_address($email) {
return filter_var($email, FILTER_VALIDATE_EMAIL) ? 1 : 0;
        }

		function error($error){
$fullerror = "<center><div id=error><h2>Error:</h2><p>
".$error."</div></center>";
die($fullerror);
}


if (isset($_POST['submit'])) {
    $username = $_POST["username"];
    $password = $_POST["password"];
     $email = $_POST["email"];

      $username = mysqli_real_escape_string($db, $username);
      $email = mysqli_real_escape_string($db, $email);
      $password = mysqli_real_escape_string($db, $password);
      $password2 = mysqli_real_escape_string($db, $password2);

      $username = addslashes($username);
      $email = addslashes($email);
      $password = addslashes($password);
	  $password2 = addslashes($password2);

      $password = md5($password);

	  if ($_POST['password']!= $_POST['password2'])
 {
     die("Oops! Password did not match! Try again. ");
 }

 if(strlen($_POST['password']) <= 3){
error('Sorry, that password was too short.');
}

 if(strlen($_POST['username']) <= 3){
error('Sorry, that username was too short.');
}


      $sql = "SELECT email FROM users WHERE email='$email'";
      $result = mysqli_query($db,$sql);
      $row = mysqli_fetch_array($result,MYSQLI_ASSOC);

	  $sql = "SELECT username FROM users WHERE username='$username'";
      $result = mysqli_query($db,$sql);
      $row = mysqli_fetch_array($result,MYSQLI_ASSOC);

      if(mysqli_num_rows($result) == 1) {
         die("Sorry...This email already exist..");
       }

   if(mysqli_num_rows($result) == 2) {
         die("Sorry...This username already exist..");
       }

       $query = mysqli_query($db, "INSERT INTO users (`id`,`name`, `nickname`, `email`, `password`)VALUES ('$username', '$email', '$password')");

       if($query) {
          echo "Thank You! you are now registered.";
       }

} else {

?>





<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<fieldset>
<legend>Registration Form</legend>
<table width="400" border="0" cellpadding="10" cellspacing="10">
<tr>
<td style="font-weight: bold"><div align="right"><label for="name">username</label></div></td>
<td><input name="username" type="text" class="input" size="25" required /></td>
</tr>
<tr>
<td style="font-weight: bold"><div align="right"><label for="email">Email</label></div></td>
<td><input name="email" type="email" class="input" size="25" required /></td>
</tr>
<tr>
<td height="23" style="font-weight: bold"><div align="right"><label for="password">Password</label></div></td>
<td><input name="password" type="password" class="input" size="25" required /></td>
</tr>
<td height="23" style="font-weight: bold"><div align="right"><label for="password">Re-enter your password</label></div></td>
<td><input name="password2" type="password" class="input" size="25" required /></td>
</tr>
<tr>
<td height="23"></td>
<td><div align="right">
  <input type="submit" name="submit" value="Register!" />
</div></td>
</tr>
</table>
</fieldset>
</form>

 <?php
}
?>