Question

Is it ok to include a break or exit command to prevent further code from executing or is this bad programming?

function index()
{
  $error = NULL;

  if ($_POST){

     // validate form
    if ($form_validated) {
        echo 'this content only';
        exit;    // or return         IS THIS BAD???
    } else {
        $error = 'form failed';
    }
 }  
  echo 'normal page on initial load';
  if ($error) { echo '<br />'.$error; }
}

Answer 1

It is OK to prevent further code from executing using exit.

Having said that, whether this is the best way to do it in this particular example is debatable. It is typical to use exit when issuing redirects:

header('Location: /foo');
exit;

In your case, there doesn’t seem to be an immediate need to stop the program execution in mid run. You should rather structure your program flow so it always completes, but with different results. It is hard to follow program logic which may terminate somewhere in the middle, so a more logical flow that returns from functions or branches using if..else is usually preferable.