这2'IF'有什么区别？

Given this:

$ids = '';

I just realized that this:

$single = $ids == FALSE || is_array($ids)? FALSE : TRUE;
var_dump($single);

and this:

if ($ids == FALSE) 
{
    $single = TRUE;     
}
else 
{
    if (is_array($ids)) 
    {
        $single = FALSE;
    } 
    else 
    {
        $single = TRUE;
    }
}
var_dump($single);

Display different results (false and true respectively). However, This only happens when the variable is:

$ids = '';

or

$ids;

If $ids is an array, an integer, or a string it works fine. Does anybody know why? Thanks in advance!

By the way, I have just realized that if you type $ids === FALSE in the first conditional stament (the single line one) it will work fine. But I still don't understand the 'logic' behind this.

You forgot parentheses:

$single = (($ids == FALSE) || (is_array($ids)? FALSE : TRUE));
var_dump($single);

// Output: true

Live demo.

Without them, precedence gives you a result different from that which you were expecting:

<?php
$id = '';

$single =  $ids ==  FALSE ||  is_array($ids)? FALSE : TRUE;
//        (        (                        )             )
//                   FALSE                    FALSE

var_dump($single); // False


$single = (($ids == FALSE) || (is_array($ids)? FALSE : TRUE));
//              TRUE       ||       FALSE

var_dump($single); // True
?>

^{Note that '' == FALSE is true; I'm not sure whether you realised that.}

I could be wrong but It may be because you are returning a Boolean Equivlenant (1 / 0) or a True and False String. If you want Absolute equality try using 3 equals symbols.

The order of operations is different in the two examples. The first one is parsed as:

$single = ( $ids == FALSE || is_array($ids) ) ? FALSE : TRUE;

The second one is equal to:

$single = ( $ids == FALSE ) || ( is_array($ids)? FALSE : TRUE );