title: PHP 7, Fatal error: Constant expression contains invalid operations
body: <p>I am building a login sequence for a website that I am designing for a school project with <strong>MySQL</strong> and <strong>PHP7</strong> (which I am relatively new to). I need some help understanding what this error means and how I can resolve the issue: </p>
  
  <blockquote>
    <p>Fatal error: Constant expression contains invalid operations in
    C:\Abyss Web Server\htdocs\login_tools.php on line 19</p>
  </blockquote>
  
  <p>Here is the line of code for a function which ensures a login has succeeded and retrieves the associated user details:</p>
  
  <pre><code>function validate($dbc, $email=",$pwd=")
  </code></pre>