vector variable value on PHP

Question

Well, ths is a really newbie question, but couldn't find the proper keywords to get the answer.

I have a vector variable, $p.

I want to achieve this:

$n = 5;

$prev = $p[$n--];
$actual = $p[$n];
$next = $p[$n++];

The values i want should be:

$prev = 4;
$actual = 5;
$next = 6;

Instead of that, i get:

$prev = 5;
$actual = 4;
$next = 4;

I know i'm missing something, but i couldn't figure it out.

Thanks in advance

Answer 1

Just do the math yourself:

$prev   = $p[$n - 1];
$actual = $p[$n];
$next   = $p[$n + 1];

If you must use increment / decrement operators (for some strange reason), you can use:

$prev   = $p[--$n];
$actual = $p[++$n];
$next   = $p[++$n];

Note that your original code was failing, as jeremy points out, because increment and decrement operators modify the original value of the variable.

Answer 2

At the first search:

$prev = $p[$n--]

You are changing the value of n for the next operations, decreasing it by one. In

$next = $p[$n++];

You are increasing it again so n value is the same as the beginning. You should do what nickb told.