C++ STL

Question

In a vector<int> v;
what is the difference between 1 and 2?
void f(vector<int>& v) {
v[0]; // 1.
v.at(0); // 2.
}

Answer 1

its better to use 2nd because you can change your data structure easily in future just by changing vector to list (for example) in definition line ; but in first one you have to replace v[] with v.at() in order to use map or list or ...

Answer 2

thx 4 d answer amir