Binary Indexed Tree or Fenwick Tree

#include<bits/stdc++.h>

#define N 10001

using namespace std;

int tree[N], a[N];

int query(int indx)

{

    int sum = 0;

    while(indx > 0)

    {

        sum += tree[indx];

        indx = indx - (indx & (-indx));

    }

    return sum;

}

void update(int indx, int value, int n)

{

    while(indx <= n)

    {

        tree[indx] = tree[indx] + value;

        indx = indx + (indx & (-indx));

    }

}

int main()

{

    int n, indx, value;

    /// here array must be greater than 4 for below operation

    cout << "Enter Array Size :: "; 

    cin >> n;

    /// add 5 in index 1

    update(1, 5, n);

    /// add 3 in index 2

    update(2, 3, n);

    /// add 1 in index 3

    update(3, 1, n);

    /// add 6 in index 4

    update(4, 6, n);

    /// add 2 in index 5

    update(5, 2, n);

    cout << "sum of index 1 to 3 is :: " << query(3) << "\n";

    cout << "sum of index 1 to 2 is :: " << query(2) << "\n";

    cout << "sum of index 2 to 4 is :: " << query(4) - query(1) << "\n";

    return 0;

}