先输出下面代码,再去掉注释执行，是两个效果

#include <bits/stdc++.h>
using namespace std;
int main(){
    vector<int > v={0,1,2,3,4,5,6};
    vector<vector<int> > xxx={{1,2,3},{4,5,6}};
    int qqq;
    for(int u=0;u<v.size();u++){
    	//qqq=xxx[1].front();xxx[1].erase(xxx[1].begin());
    	cout<<u<<endl; 
	}
	return 0;
}