segment tree

#include <iostream>
using namespace std;

int create(int l,int r,int at,int ars[],int arr[])
{

 if(l==r)
 { 
 	ars[at]=arr[l];
 	return 0;
 }
 
 create(l,(l+r)/2,at*2,ars,arr);
 create((l+r)/2+1,r,at*2+1,ars,arr);
 
 ars[at]=ars[at*2]+ars[at*2+1];
	
}


int query(int at,int L,int R,int l,int r,int ars[])
{
	if(l>R||r<L)
	 return 0;
	if(L==l&&R==r)
	 return ars[at];
	 
	int x=query(at*2,L,(L+R)/2,l,r,ars);
	int y=query(at*2+1,(L+R)/2+1,R,l,r,ars);
	
	return x+y;
}


int update(int at,int value,int position,int l,int r,int arr[],int ars[])
{   
	if(l==r&&l==position)
	{
		arr[l]=value;
		ars[at]=value;
		return 0;
	}
	
	int mid=(l+r)/2;
	
	if(position<=mid)
	 update(at*2,value,position,l,mid,arr,ars);
	else
	 update(at*2+1,value,position,mid+1,r,arr,ars);
	 
	ars[at]=ars[at*2]+ars[at*2+1];
	
}

int main() {
	int n;
	cin>>n;
	
	int arr[n+3]={},ars[n*4]={};
	
	
	for(int x=1;x<=n;x++)
	{
		cin>>arr[x];
	}

	
	create(1,n,1,ars,arr);
	
	int start,end;
	
	cout<<"enter range you want to sum"<<endl;
	cin>>start>>end;
	
	cout<<"result is: "<<query(1,1,n,start,end,ars)<<endl;
	
	
	int value,position;
	cout<<"enter value and position you want to change: "<<endl;
	cin>>value>>position;
	
	update(1,value,position,1,5,arr,ars);
	
	cout<<"after update result is: "<<query(1,1,n,start,end,ars)<<endl;
	
	
	return 0;
}