There is a catch, you should account for three situations:
1) N > 0
2) N < 0
3) N == 0 <--- 8-D.

Small assignment, but took an hour of trying.

you could just come up with the relatively less error-prone solution in one line
for(int i = 1; i!=N+2*(N>0)-1; i+=2*(N>0)-1) sum+=i;

Edited by author 16.11.2013 15:47