为什么下述写法1无法运行但是2可以。

#include<bits/stdc++.h>
using namespace std;
#define ll long long
int n,q;
const int N=2e5+10;
ll a[N];
struct BIT{
	ll t[N];
	void add(ll x,ll v){
		for(;x<=n;x+=x&(-x))t[x]^=v;
	}
	ll qry(ll x){
		ll res=0;
		for(;x;x-=x&(-x))res^=t[x];
		return res;
	}
};
int main(){
	cin>>n>>q;
	BIT t,t2;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		if(i%2)t.add(i,a[i]);
		else t2.add(i,a[i]);
	}
	while(q--){
		int op;cin>>op;
		int x,y;cin>>x>>y;
		if(op==1){
			if(x%2){
				t.add(x,a[x]^y);
				a[x]=y;
			}
			else{
				t2.add(x,a[x]^y);
				a[x]=y;
			}
		}
		else{
			if((y-x+1)%2==0){cout<<"0\n";continue;}
			if(x%2)cout<<(t.qry(y)^t.qry(x-1))<<"\n";
			else cout<<(t2.qry(y)^t2.qry(x-1))<<"\n";
		}
	}
	return 0;
} 

#include<bits/stdc++.h>
using namespace std;
#define ll long long
int n,q;
const int N=2e5+10;
ll a[N];
struct BIT{
	ll t[N];
	void add(ll x,ll v){
		for(;x<=n;x+=x&(-x))t[x]^=v;
	}
	ll qry(ll x){
		ll res=0;
		for(;x;x-=x&(-x))res^=t[x];
		return res;
	}
};
BIT t[2];
int main(){
	cin>>n>>q;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		t[i&1].add(i,a[i]);
	}
	while(q--){
		int op;cin>>op;
		ll x,y;cin>>x>>y;
		if(op==1){t[x&1].add(x,a[x]^y),a[x]=y;}
		else{
			if((y-x+1)%2==0){cout<<"0\n";continue;}
			cout<<(t[x&1].qry(y)^t[x&1].qry(x-1))<<"\n";
		}
	}
	return 0;
} 

我是奶龙