C++: What is the difference between std::array and std::vector?

1// array — compile-time size
2std::array<int, 3> arr = {1, 2, 3};
3// arr.push_back(4);  // Error!
4
5// vector — runtime size
6std::vector<int> v = {1, 2, 3};
7v.push_back(4);  // OK