#include<vector>
#include<algorithm>
// all the std and main syntax ofcourse.
vector<int> pack = {1,2,3} ;
// To add at the END
pack.push_back(6); // {1,2,3,6}
// OR
// To add at BEGGINING
pack.insert(pack.begin(),6) // {6,1,2,3,}
//vector.push_back is the function. For example, if we want to add
//3 to a vector, it is just vector.push_back(3)
vector <int> vi;
vi.push_back(1); //[1]
vi.push_back(2); //[1,2]