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 = $th         


        

Answer 1

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;