BIT -- POINT INCREASE AND RANGE QUERY !!!!

https://www.youtube.com/results?search_query=binary+index++tree videotutorial
BIT -- POINT INCREASE AND  RANGE QUERY !!!!

QUERY CAN BE OF TYPE SUM FROM INDEX 0 TO A ..

NOTE WE CAN CHANGE QUERY AS SUM FROM [a,b] IF WE CALL QUERY 2 TIMES 
ie- query(b)-query(a-1).
-------------------------------------------CODE---------------------------------------------------------------------
#include<iostream>
using namespace std;
#include<bits/stdc++.h>
 int arr[10000000];
  int tree[1000000];
   int n;

  // build tree
void build(int val,int index)
 {

  while(index<=n)
  {
 
  tree[index]+=val;
  index+=index & (-index);
 
 }
 }


 // increase ith index value by val ..
 void update(int val,int index)
  {



    while(index<=n)
  {
 
  tree[index]+=val;
  index+=index & (-index);
 
 }
  }

  // sum from index 1 to index
   int query(int index)
    {
   
    int sum=0;
    while(index!=0)
     {
      sum+=tree[index];
      index-=index & (-index);
 }
 return sum;
}


 int main()
  {
 
   cin>>n;
    for(int i=1;i<=n;i++)
     {
      cin>>arr[i];
 }

 for(int i=1;i<=n;i++)
  {
  build(arr[i],i);
  }

  int q;
   cin>>q;
   while(q--)
    {
    int type ;
     cin>>type;
     if(type==1)
      {
       int val ,index;// index   at which need to update if array is 1 based
       cin>>val>>index;
       update(val,index);
       cout<<" tree status "<<endl;
       for(int i=1;i<=n;i++) cout<<tree[i]<<" ";
       cout<<endl;
}
else
{
int index;
 cin>>index;// sum of fist index no of numbers ...
int ans=query(index);
cout<<ans<<endl;
}
}
 
  }