Question

Is there a way of using the compound assignment operator to achieve something like this:

a = (a * 10) + b;

Initially I tried the following:

a *= 10 + b;

but this is equivalent to:

a = a * (10 + b)

Just curious. Ran across this today. This is not homework.

Answer 1

If you really need to make sure a is evaluated only once, you could use the fact that *= returns lvalue:

(a *= 10) += b;

but it’s hardly good code, and I think it might be invoking undefined behaviour prior to C++11 due to modifying a twice (once in *= and once in +=) without intervening sequence points.