Question

Can someone explain the logic behind this for loop… I just don’t get it on how it goes into the next element, that $from[$i], what is it doing?

$start = 2;

$path = array();
for (; $i != $start; $i = $from[$i])
         $path[] = $i;

Answer 1

It’s not very clearly written. I assume $i and $start are previously initialized.

Basically, there is no for loop initialization. It continues until $i equals $start. In the body, $i is appended to the $path array. Before going to the next iteration, $i is set to the value of the $i key in $from.

So if the array looked like:

$from = array('foo'=>'bar', 'bar'=>'baz', 'baz'=>'goo');

and $i are $start are ‘foo’ and ‘goo’ respectively, $path will end up:

array('foo', 'bar', 'baz')

If $start is unreachable, it will loop forever.