0分求助

#include<bits/stdc++.h>
using namespace std;
queue<int> q;
int n,a,x;
int main() {
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a;
		if(a==1)
		{
			cin>>x;
			q.push(x);
		}
		else if(a==2)
		{
			if(q.empty()) cout<<"ERR_CANNOT_POP";
			else q.pop();
		}
		else if(a==3)
		{
			if(q.empty()) cout<<"ERR_CANNOT_QUERY";
			else cout<<q.front();
		}
		else if(a==4) cout<<q.size();
		cout<<endl;
	}
	return 0;
}