Fenwik Tree

#include<bits/stdc++.h>
using namespace std;
void update(int index, int delta, vector<int>& vc) {
    while (index < vc.size()) {
        vc[index] += delta;
        index = index | (index + 1);
    }
}
int sum(int index, vector<int>& vc) {
    int s = 0;
    while (index >= 0) {
        s += vc[index];
        index = (index & (index + 1)) - 1;
    }
    return s;
}
int sum(int l, int r, vector<int>& vc) {
    return sum(r, vc) - sum(l - 1, vc);
}
int main() {
    int n;
    cin >> n; // size of vector
    vector<int> vc(n, 0);
    int tmp;
    for (int i = 0; i < n; ++i) { // first setup of vector
        cin >> tmp;
        update(i, tmp, vc);
    }
    int c; //count of requests
    cin >> c;
    string stmp;
    int l, r, in, d;
    for (int i = 0; i < c; ++i) {
        cin >> stmp;
        if (stmp == "ADD") {
            cin >> in >> d;
            update(in - 1, d, vc);
        } else if (stmp == "SUM") {
            cin >> l >> r; // l <= r
            cout << sum(l - 1, r - 1, vc) << '\n';
        }
    }
}