What does `$page -= 1` in my PHP document mean?

Question

I have the following variable defined in a PHP document I am working with, and I'm unsure what it means.

The PHP

$page -= 1;

The part I am unsure of is the -=

score 7 · Answer 1 · answered Aug 21 '11 at 18:24

7

It's a shorthand to save typing. It's effect is idential to

$page = $page - 1;

answered Aug 21 '11 at 18:24

Peder Klingenberg

score 3 · Accepted Answer · answered Aug 21 '11 at 18:27

3

The -= operator is shorthand for subtracting a value from the variable:

$x -= 1;
$x = $x - 1;

Here's some of the other ones:

answered Aug 21 '11 at 18:27

Blender

Very very helpful. Thanks so much! I commented on the answer above. Think you can shed some light on that? – stefmikhail Aug 21 '11 at 18:28
1

`$page` is only defined once. If I do `x = 1` and `x = 2`, `x` is equal to `2` because that is the last value I told `x` to be. BTW, `x = 1` and `1 = x` are not the same thing, so `$cur_page = $page;` is setting `$cur_page`, not `$page`. – Blender Aug 21 '11 at 18:30
Thanks for the clarification. Also, your answer was thorough and will be quite helpful in my future endeavours with PHP. – stefmikhail Aug 21 '11 at 18:42
What would `"page="+page` mean? – stefmikhail Aug 21 '11 at 21:55

score 1 · Answer 3 · answered Aug 21 '11 at 18:24

1

The -= operator is a combination arithmetic and assignment operator. It subtracts 1 then reassigns it to $page.

answered Aug 21 '11 at 18:24

So in my document, the following variables are defined: `$page = $_GET['page']; $cur_page = $page; $page -= 1;` How can `$page` be defined as three different things? – stefmikhail Aug 21 '11 at 18:26
2

It's defined once (the first time it occurs) and then operations are performed that modify it's value. So if `$_GET['page']` equals 10, then `$page` will equal `10` as well after `$page = $_GET['page'];`, then `$cur_page` will also be assigned a value of `10` and finally value of `$page` will be reduced to `9` after `$page -= 1;` – Mchl Aug 21 '11 at 18:31
@Mchl One question. I'm guessing the reason the code isn't just `$page -= $_GET['page']` is for the `$cur_page` variable to be defined as the current page, correct? I suppose I could also use a different variable, i.e.. `$page_minus_one = $page - 1`, am I correct? – stefmikhail Aug 21 '11 at 18:46

score 1 · Answer 4 · answered Aug 21 '11 at 18:25

1

It's the same as $page = $page - 1, $page-- or --$page, it's used to decrement the value of the variable.

answered Aug 21 '11 at 18:25

Mark Tomlin

1

Careful about `$page--` and `--$page`. They're almost, but not quite the same. – Mchl Aug 21 '11 at 18:32
1

Yes, one get's decremented before the copy, when happens after, but the statements by themselves are effectively the same when used on a line all by themselves. – Mark Tomlin Aug 21 '11 at 18:34

4 Answers4