seq tree without seq update

#include <bits/stdc++.h>
#define endl "\n"

using namespace std;
using ll = long long;
using pii = pair<int, int>;

constexpr int N = 5e6+1;
constexpr int MOD = 1e9+7;
constexpr int INF = 1e9+9;

int tr[4*N], n, arr[N], q, ql, qr;
char type;

void build(int id = 0, int l = 0, int r = n)
{
  if (l==r)
    return;
  if (l+1==r)
  {
    tr[id]=arr[l];
    return;
  }
  int mid = (r+l)/2;
  build(2*id+1, l, mid);
  build(2*id+2, mid, r);
  tr[id]+=tr[2*id+1]+tr[2*id+2];
}

void upd(int val, int i, int id = 0, int l = 0, int r = n)
{
  if (l==r)
    return;
  if (l+1==r)
  {
    tr[id]+=val;
    return;
  }
  tr[id]+=val;
  int mid = (l+r)/2;
  if (i<mid)
    upd(val, i, 2*id+1, l, mid);
  else upd(val, i, 2*id+2, mid, r);
}

void update(int i, int val)
{
  i--;
  int temp = val-arr[i];
  arr[i]=val;
  val = temp;
  upd(val, i);
}

int get(int l, int r, int id = 0, int cl = 0, int cr = n)
{
  if (l>cr||r<cl||l==r)
    return 0;
  if (l==cl&&r==cr)
  {
    return tr[id];
  }
  int mid = (cl+cr)/2;
  return get(max(l, cl), min(r, mid), 2*id+1, cl, mid)+
  get(max(l, mid), min(r, cr), 2*id+2, mid, cr);
}

int get_sum(int l, int r)
{
  l--;
  return get(l, r);
}

int close(int n)
{
  int res = 1;
  while(res<n)
  {
    res<<=1;
  }
  return res;
}
void Solve()
{
  cin >> n >> q;
  for (int i = 0; i < n; i++)
    cin >> arr[i];
  n=close(n);
  build();
  while(q--)
  {
    cin >> type >> ql >> qr;
    if (type=='=')
      update(ql, qr);
    else cout << get_sum(ql, qr) << endl;
  }
}

int main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  Solve();
  return 0;
}