std::vector is a dynamic array container that can resize itself automatically when an element is inserted or deleted. It provides contiguous storage and efficient access.

Almost always when you need a list or array. It is the default container of choice in C++ due to its cache friendliness and performance.

• Access: $O(1)$
• Push Back: $O(1)$ amortized.
• Insertion/Deletion (middle): $O(N)$

cpp Standard
#include <vector>
#include <iostream>

std::vector<int> v = {1, 2, 3};
v.push_back(4); // Adds 4 to end
std::cout << v.size(); // 4
for (int x : v) std::cout << x << " ";

• Not using v.reserve() when the number of elements is known, leading to multiple reallocations.
• Using v[i] without checking bounds (use v.at(i) for safety).
• Erasing elements inside a manual loop without correctly updating the iterator.