i don't understand while ($x=somefunction())

koen

Actually I think I have problems understanding the truth value of an assignment. The while keeps looping until the expression contained within it ($x=somefunction()) returns false.

So is the value of ($x=5) 5? And is it only false when somefunction returns nothing (or false)? And if ($x=5) has 5 as value, is 5 also TRUE (otherwise the while loop wouldn't run)?

Andrew_W_Peace

When a variable is being assigned a value, if it works it returns 1. If it does not work it returns 0. In other words, if you are doing

while($x=5)

It will ALWAYS return 1 (true). However, if you are doing something like

while($x=somefunction())

It might not. If the function works and returns something to $x, then it will return 1. If it fails and does not return anything to $x, it will return 0 (false), so it will stop. The real reason you'd want to use a loop is for a conditional. For example, if you do this:

$x=0;
while($x>5)
{
print $x;
$x++;
}

That loop checks to see if $x is greater than five yet. If it is, the loop stops. If it's not it keeps going.

Installer

...if it works it returns 1.

Not necessarily. The operation itself returns a value (in the case of your example 5, not 1), which is what the conditional evaluates rather than the "success" of the operation. For example, if the result of the assignment is 0:

$i = 5;
while ($x = $i--) {
    echo $x . '<br />';
}

The loop is exited at zero, and "0" isn't displayed, since it is evaluated as false. The same would be true of an empty string, a null type (i.e. NULL), and even an empty array.

Add-on: This code shows that any operation returns its value:

$x = 5;
while (1 * --$x) {
    echo $x . '<br />';
}

Again the loop exits when the operation returns zero.