Hello Alexan:
First the postfix and prefix operators are evaluated and the added together as they have higher precedence over addition.
So coming back to your question:
int x = -1;
y = x++ + ++x;
This would be evaluated as:
y = -1 + 1
y = 0
The postfix operator (x++) gets the value -1 first and then x is incremented by 1 to give 0.
The prefix operator (++x) adds 1 to x first, then uses the new value of x as the value of the expresiion.
Hope this helps.
Emad