STL vector

<img src="http://img.blog.csdn.net/20160409141926978" alt="" />

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;
//using std::vector;
vector<int>a(1);
int main()
{
	int n,x,m;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>x;
		a.push_back(x);
	}
	cout<<a.size();
	cin>>m;
	cout<<a.at(m)<<endl;
	cout<<"first"<<a.front()<<endl;
	cout<<"last"<<a.back();
	 
}