Empty container constructor
vector<int> vec;
Fill constructor (4 int with value 20)
vector<int> vec(4, 20);
Range constructor
int arr[] = {1, 2, 3, 5, 2, 6}
vector<int> vec(arr, arr+6);
Copy constructor
vector<int> myvec(vec);
Another way
vector<int> vec {1, 2, 3, 4};