Are there any drawbacks in usage of deque instead of vector

Is it possible to write Fenwick tree for sum in segment and for update(+val) in segment? And is it optimally?

I have a lot of files named with sample numbers 1, 2, 3 and so on. In this files there are two integers a and b. And I should print a+b. And output should be in files such as 1.a, 2.a, 3.a etc.

Please, help me or send me correct code. Code;

This code create answer for 1st file. But for others, outputs answer of 1st file too.

P.s. Sorry for my English.