Vectors & Sequence Containers

std::vector is a dynamically-growable array — the everyday default sequence container, playing the same role Java's ArrayList does.

#include <vector>

std::vector<int> numbers = {1, 2, 3};
numbers.push_back(4);
std::cout << numbers[0] << std::endl;  // 1
std::cout << numbers.size() << std::endl; // 4

for (int n : numbers) {
    std::cout << n << " ";
}

Other sequence containers exist for specific needs: std::array<T, N> (a fixed-size array with bounds-checked .at()), std::deque (efficient push/pop at both ends), and std::list (a doubly-linked list) — but vector should be the default choice unless a specific need points elsewhere.

Common mistakes

• Using [] when out-of-bounds safety matters — like a C array, [] on a vector does no bounds checking. Use .at(index) instead, which throws std::out_of_range on an invalid index.

Practice

Create a std::vector<int>, add the numbers 1 through 5, and print their sum using a range-based for loop.

std::vector<int> nums = {1, 2, 3, 4, 5};
int sum = 0;
for (int n : nums) {
    sum += n;
}
std::cout << sum << std::endl; // 15