vector

A dynamic array that grows automatically — the default container in C++.

Easy

#include <vector>
std::vector<int> v = {3, 1, 2};
v.push_back(4);
v.size();          // 4
v[0];              // 3 (no bounds check) — v.at(0) checks
for (int x : v) std::cout << x << ' ';
v.reserve(1000);   // pre-allocate to avoid repeated reallocations

Elements are stored contiguously, so access is fast and cache-friendly. Adding to the end is fast on average; inserting in the middle is slow.

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