宏观定义：
a sequence container that encapsulates dynamic size arrays.

与数组的区别：
Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted.

Create a vector containing integers:

#include <vector>
std::vector<int> v = {7, 5, 16, 8};