Question

Can you make an assignment on conditional statement in php as so:

if(siteName_err = isValid("sitename", $_POST['sitename'], false))
{
    $siteName = $_POST['sitename'];
}

Answer 1

Yes.

I think the most common use scenario for this is when using MySQL. For example:

$result = mysql_query("SELECT username FROM user");
while ($user = mysql_fetch_assoc($result)) {
  echo $user['username'] . "\n";
}

This works because $user is the result from the assignment. Meaning, whatever is stored in your assignment, is then used as the conditional. In other words,

var_dump($i = 5);

// is equivalent to

$i = 5;
var_dump($i);

Both will print int(5), obviously.