a += ++a logic

Question

Let's look at this code
int a = 2;
a += ++a;
cout << a;

I expect the output to be 5 but the real output is 6.
I don't understand this.
Doesn't it has same meaning as:
a = a + ++a? (shouldn't the first 'a' be the original value? )

Answer 1

I think this happens because expression a+=b can be also defined as a=a+(b);
Because this will make sense if we assume it as a=a+(++a)

https://code.sololearn.com/cufOX0HNd9fY/?ref=app

Or maybe ~ swim ~ is right it can be sequence point also

Answer 2

In Java, result a=5 only...
with clear expression evaluation is left to right associative..
Edit:
Output is compiler specific in c/c++. You may get different outputs in different compilers.