std::vector (and when std::array)

#include <vector>

std::vector<int> scores;                 // empty
scores.push_back(9);                     // append: {9}
scores.push_back(7);                     // {9, 7}
std::vector<int> init{9, 7, 10};         // initializer list
std::vector<int> filled(5, 0);           // {0,0,0,0,0} — five zeros

Why vector beats raw arrays

A raw C array int a[10] is a fixed block of bytes: no size knowledge, no bounds checks, decays to a pointer when passed, and cannot grow. std::vector is a resizable array that knows its own length, copies properly on assignment, and cleans up after itself (that last point is RAII — module 12). Rule of thumb with almost no exceptions: if you are writing a raw array, you probably want a std::vector (known size) or std::array (fixed small size).

std::array<int, 3> is a thin wrapper over a fixed-size array that adds the standard-library conveniences (.size(), comparisons, STL algorithm compatibility) with zero overhead. Use it when the size is genuinely fixed at compile time.

The everyday API

scores.size()            // 2 — a size_t (unsigned); watch int/size_t comparisons
scores.at(1)             // 7 — bounds-checked; [] is the unchecked fast path
scores.back()            // 10
scores.pop_back()        // remove last
scores.empty()           // false

Iterating

for (int s : scores) { /* by value — copies each int */ }
for (const int& s : scores) { /* read-only, no copy */ }
for (int& s : scores) { s *= 2; }        // mutate in place

The const& form matters when elements are big (strings); for ints it is a wash. Module 11 explains the & fully.

Growth and 2-D

push_back occasionally grows the vector's buffer (capacity ≥ size) — you do not manage that; just know size() is elements, capacity() is room. A 2-D grid is a vector of vectors: std::vector<std::vector<int>> grid(rows, std::vector<int>(cols, 0)); then grid[r][c] (bounds-checked: grid.at(r).at(c)).