Help me explain b= a-- + --a and b= --a + a--

Question

Hi guys, can you explain that cases for me?
1.
int main() {
int a= -5;
int c = --a + a--;
cout<<a;
}

// I dont understand why the answer is c = -13. I think it must be c = -12.

2.
int main() {
int a= -5;
int c = a-- + --a;
cout<<a;
}
//The answer is c = -12. I don't understand! Please help me.

Answer 1

Are you sure that the last row in both examples Is "cout << a" not "cout << c"?

If it "cout << c" than the first example:

(-5-1) + (-6) = -12 --> Also don't know why -13 but I think that you have mistyped example or just I don't know...

And second:

(-5) + (-6-1) = -12

Answer 2

The behaviour of programs with multiple prefix/postfix operators between two sequence points is undefined.

https://stackoverflow.com/questions/4176328/undefined-behavior-and-sequence-points

Answer 3

https://www.sololearn.com/discuss/523078/?ref=app

Answer 4

@hatsy is right answer completly depends on compiler

Answer 5

@Ondrej Donek : Thank you. I have mistyped. It is " cout<<c; ". Sorry I can't write your name exactly!

Answer 6

@Minh - No problem with name - our Czech language is strange but beautiful! :) Have a nice day.

Answer 7

Thank everyone.