What type of error is this? Plz coreect it in the following code.

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PHP

( ! ) Parse error: syntax error, unexpected ':' in E:\wamp\www\my own\checklogin.php on line 11

<?php
    session_start();
    $username = mysql_real_escape_string($_POST['username']);
    $password = mysql_real_escape_string($_POST['password']);
    $bool = true;

    mysql_connect("localhost", "root", "") or die (mysql_error()); //Connect to server
    mysql_select_db("first_db") or die ("Cannot connect to database"); //Connect to database
    $query = mysql_query("Select * from users WHERE username='$username'"); // Query the users table
    $exists = mysql_num_rows($query); //Checks if username exists
    $users = "":
    $password = "";
    if($exists > 0) //IF there are no returning rows or no existing username
    {
       while($row = mysql_fetch_assoc($query)) // display all rows from query
       {
          $users = $row['username']; // the first username row is passed on to $table_users, and so on until the query is finished
          $password = $row['password']; // the first password row is passed on to $table_password, and so on until the query is finished
       }
       if(($username == $users) && ($password == $password))// checks if there are any matching fields
       {
          if($password == $password)
          {
             $_SESSION['user'] = $username; //set the username in a session. This serves as a global variable
             header("location: home.php"); // redirects the user to the authenticated home page
          }
       }
       else
       {
        Print 'alert("Incorrect Password!");'; // Prompts the user
        Print 'window.location.assign("login.php");'; // redirects to login.php
       }
    }
    else
    {
        Print 'alert("Incorrect username!");'; // Prompts the user
        Print 'window.location.assign("login.php");'; // redirects to login.php
    }
?>

What I have tried:

i also paste the code in which this error exist. plz correct it