What is the meaning of b - = a+ in c++

Question

it is really uncommon in my previous studies in this language

Answer 1

i guess that this will make a compile error, but "b -= a++;" will give rhe answer. So i will stick to that.
-= is a fancy and simpler way of saying b = b - a.
the same goes to +=, *=, /=

Answer 2

The second part of your answer is what I am seeking