What is += used for?

Question

I think this is a dumb question but I could not find it on php. Why is a + with the = in the following code:

function calculateRanking()
{
    $created = $this->getCreated();

    $diff = $this->getTimeDifference($created, date('F d, Y h:i:s A'));

    $time = $diff['days'] * 24;
    $time += $diff['hours'];
    $time += ($diff['minutes'] / 60);
    $time += (($diff['seconds'] / 60)/60);

    $base = $time + 2;        

    $this->ranking = ($this->points - 1) / pow($base, 1.5);

    $this->save();
}

Is this so $time has all those values or rather it is adding all the values to $time?

Thanks

Answer 1

$time += $diff['hours'];

is the same as saying

$time = $time + $diff['hours'];

Answer 2

It's adding all those values to time.

something += somethingelse

is a shortcut for

something = something + somethingelse

Answer 3

a += 2; is the equivalent of a = a + 2;

At one time with some languages (especially very old C compilers), the compiler produced better code with the first option. It sticks around now because it's a common idiom and people used to it think it's clearer.

Answer 4

x += 10 is simply a shorter way to write x = x + 10.

In this case, the code is finding the time difference in hours from a time difference structure.

Answer 5

Shortcut operator for $val = $val + $otherval.

This only works on numeric values

Answer 6

Let's replace a few things to make it a bit easier to understand.

The += is just the same as below:

$time = $diff['days'] * 24;
$time = $time + $diff['hours'];
$time = $time + ($diff['minutes'] / 60);
$time = $time + (($diff['seconds'] / 60)/60);

Answer 7

There are lots of these shorthand operators in C, C++ in other modern languages.

a -= b;   // a = a - b;
a *= b;   // a = a * b;
a &= b;   // a = a & b;

etc., etc., etc.

Answer 8

Also, "a += b" is an expression who's value can be used again immediately,

(((((a += b) *= c) += d) * e) += f);

is a lot less typing than

a = a + b;
a = a * c;
a = a + d;
a = a * e;
a = a + f;

Answer 9

I just wanted to add that this information is, indeed, on PHP's website in the section on operators, or more specifically, assignment operators.