I have been trying to follow a guide for making a PHP server app and I am getting a few syntax errors.

Error message: 

```
Parse error: syntax error, unexpected '?' in 
D:\inetpub\wwwroot\cmpswoo1\CMPPROJ_Web\ServerApp\api2\db_functions2.php on line 134 

```

So I know were the error is, I just don't know how to fix it 

```
<?php
class db_functions2 {
private $db;
//put your code here
// constructor
function __construct() {
    require_once 'db_connect2.php';
    // connecting to database
    $this->db = new db_connect2();
    $this->db->connect();
}
// destructor
function __destruct() {
}
/**
 * Random string which is sent by mail to reset password
 */
public function random_string()
{
$character_set_array = array();
$character_set_array[] = array('count' => 7, 'characters' => 'abcdefghijklmnopqrstuvwxyz');
$character_set_array[] = array('count' => 1, 'characters' => '0123456789');
$temp_array = array();
foreach ($character_set_array as $character_set) {
    for ($i = 0; $i < $character_set['count']; $i++) {
        $temp_array[] = $character_set['characters'][rand(0,  strlen($character_set['characters']) - 1)];
    }
 }
 shuffle($temp_array);
 return implode('', $temp_array);
 }
 public function forgotPassword($forgotpassword, $newpassword, $salt){
 $result = mysql_query("UPDATE `Users` SET `encryptedPassword` = '$newpassword',`salt` = '$salt'
          WHERE `email` = '$forgotpassword'");
 if ($result) {
 return true;
 }
 else
 {
 return false;
 }
 }
 /**
 * Adding new user to mysql database
 * returns user details
 */
 public function storeUser($FirstName, $LastName, $DOB, $email, $Username, $Password) {
    $uuid = uniqid('', true);
    $hash = $this->hashSSHA($Password);
    $encrypted_password = $hash["encrypted"]; // encrypted password
    $salt = $hash["salt"]; // salt
    $result = mysql_query("INSERT INTO Users(unique_id, FirstName, LastName, email, DOB, Username, encryptedPassword, salt, created_at) VALUES('$uuid', '$FirstName', '$LastName', '$email', '$DOB', '$Username', '$encryptedPassword', '$salt', NOW())");
    // check for successful store
    if ($result) {
        // get user details
        $uid = mysql_insert_id(); // last inserted id
        $result = mysql_query("SELECT * FROM Users WHERE uid = $id");
        // return user details
        return mysql_fetch_array($result);
    } else {
        return false;
    }
}
 /**
 * Verifies user by username and password
 */
 public function getUserByUsernameAndPassword($Username, $Password) {
    $result = mysql_query("SELECT * FROM Users WHERE usernameE = '$Username'") or die(mysql_error());
    // check for result
    $no_of_rows = mysql_num_rows($result);
    if ($no_of_rows > 0) {
        $result = mysql_fetch_array($result);
        $salt = $result['salt'];
        $encrypted_password = $result['encryptedPassword'];
        $hash = $this->checkhashSSHA($salt, $Password);
        // check for password equality
        if ($encryptedPassword == $hash) {
            // user authentication details are correct
            return $result;
        }
    } else {
        // user not found
        return false;
    }
 }
 /**
 * Checks whether the username is valid or fake
 */
 public function validUsername($Username)
 {
 $isValid = true;
 $atIndex = strrpos($Username, "@");
 if (is_bool($atIndex) && !$atIndex)
 {
  $isValid = false;
 }
 else
 {
  $domain = substr($Username, $atIndex+1);
  $local = substr($Username, 0, $atIndex);
  $localLen = strlen($local);
  $domainLen = strlen($domain);
  if ($localLen < 1 || $localLen > 64)
  {
     // local part length exceeded
     $isValid = false;
  }
  else if ($domainLen < 1 || $domainLen > 255)
  {
     // domain part length exceeded
     $isValid = false;
  }
  else if ($local[0] == '.' || $local[$localLen-1] == '.')
  {
     // local part starts or ends with '.'
     $isValid = false;
  }
  else if (preg_match('/\.\./', $local))
  {
     // local part has two consecutive dots
     $isValid = false;
  }
  else if (!preg_match('/^[A-Za-z0-9\-\.]+$/', $domain))
  {
     // character not valid in domain part
     $isValid = false;
  }
  else if (preg_match('/\.\./', $domain))
  {
     // domain part has two consecutive dots
     $isValid = false;
  }
   else if
     (!preg_match('/^(\\.|[A-Za-z0-9!#%&`_=\/$'*+?^{}|~.-])+$/',str_replace("\\","",$local)))
  {
     // character not valid in local part unless
     // local part is quoted
     if (!preg_match('/^"(\\"|[^"])+"$/',
         str_replace("\\","",$local)))
     {
        $isValid = false;
     }
  }
  if ($isValid && !(checkdnsrr($domain,"MX") ||checkdnsrr($domain,"A")))
  {
     // domain not found in DNS
     $isValid = false;
  }
 }
 return $isValid;
 }
 /**
 * Check user is existed or not
 */
 public function isUserExisted($Username) {
    $result = mysql_query("SELECT Username from Users WHERE Username = '$Username'");
    $no_of_rows = mysql_num_rows($result);
    if ($no_of_rows > 0) {
        // user existed
        return true;
    } else {
        // user not existed
        return false;
    }
 }
 /**
 * Encrypting password
 * returns salt and encrypted password
 */
 public function hashSSHA($Password) {
    $salt = sha1(rand());
    $salt = substr($salt, 0, 10);
    $encrypted = base64_encode(sha1($Password . $salt, true) . $salt);
    $hash = array("salt" => $salt, "encrypted" => $encrypted);
    return $hash;
 }
 /**
 * Decrypting password
 * returns hash string
 */
 public function checkhashSSHA($salt, $Password) {
    $hash = base64_encode(sha1($Password . $salt, true) . $salt);
    return $hash;
 }
 }

 ?>

```