Regarding pre and post increment.

Question

can you please check my code"test" and explain the reason for difference in the output.

Answer 1

Yeah, for "i=1; ++i = ++i + i;" : the first prefix increment operator "++i" increments i by 1 BEFORE the expression happens. So now i == 2, but when assigning "++i + i" to i, the second "++i" increases i again by 1 BEFORE the expression happens. Now i = 3, therefore i = 3 + 3 = 6.
For "j=1; ++j +=j;" : the "++j" increases j by 1 BEFORE the expression happens, so now j = 2. The expression "j+=j" or "j = j + j" is equivalent to j = 2 + 2 = 4.

Answer 2

thanks for you answer @antek
you made it very clear to me.