Quiz Entry - updated: 2026.07.14
How do you declare and use a vector in C++?
#include <vector>, declare vector<int> v;, add with v.push_back(x), and index with v[i] — it's a resizable array.
#include <vector>
using namespace std;
vector<int> v; // empty vector of ints
v.push_back(10); // append elements
v.push_back(20);
cout << v[0]; // 10
cout << v.size(); // 2
Common operations:
| Operation | Code |
|---|---|
| Create empty | vector<int> v; |
| Create with size | vector<int> v(10); |
| Create with values | vector<int> v = {1, 2, 3}; |
| Add element | v.push_back(x); |
| Access element | v[i] or v.at(i) |
| Size | v.size() |
| Iterate | for (int x : v) { ... } |
Tip: vector grows automatically as you push_back, so it replaces raw dynamic arrays — no manual new[]/delete[]. Use v.at(i) when you want bounds-checking (it throws on out-of-range); v[i] does not.
Go deeper:
std::vector — cppreference — the complete vector interface.- Introduction to std::vector — LearnCpp — a beginner-friendly walkthrough.