Why does this equal 9?

Question

int i = 3;
i = ++i + i++;

++i and i++ result in 4 and 3 when alone.
So why is i++ incrementing the value when combined with ++i.

i = 4 + i++; results in 7

Edit: To everyone saying the i++ increments it to 5, why does it only increment in this specific case?

Answer 1

First ++i is 4. Second i++ is 5. Then sum them up

Answer 2

Actually, `++i + i++` doesn't equal anything! It is undefined behaviour, and those are words that every C++ programmer is scared of.

The thing is that both `++i` and `i++` produce so-called "side effects", that is, they increment the value of `i`, and the C++ standard gives no guarantee about what side of the `+` operator is executed first. Undefined behaviour means you may likely see different compilers give different results, so you can't rely on it yielding `9` at all.

Answer 3

when I is defined to be ++I + I++ , I is incremented once cos of the pre-increment and the value of ++I and I++ is 4.. and then , when you print it.. the post-increment statement is done in the cout statement and we get 4+4+1 is equal to 9