#include <vector>
vector<int> vec(2),vec2;
vec[0]=2;
vec[1]=3;
vec.resize(1024*1024);
int m = *vec.begin();
m = * vec.end();
m = vec2.size();
//vec2[0]=23; //error
if(vec2.empty())
vec2.resize(3);
m = vec2.size();
if(vec2.empty())
vec2.resize(5);
m = vec2.size();
vec.back();