C++ Vectors

What is a Vector?

A vector is a dynamic array that can grow or shrink at runtime. It is the most commonly used STL container.

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> scores;

    scores.push_back(90);
    scores.push_back(85);
    scores.push_back(78);
    scores.push_back(92);

    cout << "Size: "     << scores.size()  << endl;
    cout << "First: "    << scores.front() << endl;
    cout << "Last: "     << scores.back()  << endl;
    cout << "Index 2: "  << scores[2]      << endl;

    scores.pop_back();   // removes last
    cout << "After pop: " << scores.size() << endl;

    for (int s : scores) cout << s << " ";
    cout << endl;
    return 0;
}

Output:

Size: 4
First: 90
Last: 92
Index 2: 78
After pop: 3
90 85 78

Key Vector Operations

vector<string> fruits = {"Apple", "Banana", "Cherry"};
fruits.insert(fruits.begin() + 1, "Blueberry");
fruits.erase(fruits.begin());   // removes "Apple"
for (const string& f : fruits) cout << f << " ";
// Blueberry Banana Cherry

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> nums;
    int n;
    cout << "Enter numbers (0 to stop): " << endl;
    while (cin >> n && n != 0) nums.push_back(n);

    if (nums.empty()) { cout << "No numbers entered." << endl; return 0; }

    double sum = 0;
    for (int x : nums) sum += x;
    cout << "Average: " << sum / nums.size() << endl;
    return 0;
}

Summary

• vector is a dynamic array that resizes automatically.
• Key operations: push_back, pop_back, insert, erase, size, clear.
• Prefer at(i) over [i] for bounds-checked access.