C++ vector Tutorial

The C++ Standard Template Library (STL) provides the vector container for creating dynamic arrays. Unlike static arrays, vector can grow or shrink in size during runtime, making it a versatile choice for managing collections of elements.

Key Features of vector

  1. Defined in <vector> header.
  2. Dynamic sizing: Automatically resizes when elements are added or removed.
  3. Random access: Access elements using the subscript operator [].
  4. Rich functionality: Provides a range of member functions like push_back, pop_back, and size.

1. Declaring a vector

You can declare a vector with any data type:

#include <iostream>
#include <vector> // Required for vector

using namespace std;

int main() {
    vector<int> myVector; // Declare an empty vector of integers
    return 0;
}

2. Initializing a vector

You can initialize a vector in different ways:

#include <iostream>
#include <vector>

using namespace std;

int main() {
    vector<int> v1;             // Empty vector
    vector<int> v2(5, 10);      // 5 elements, each initialized to 10
    vector<int> v3 = {1, 2, 3}; // Using initializer list
    vector<int> v4(v3);         // Copy constructor

    // Printing v2
    cout << "v2: ";
    for (int x : v2) {
        cout << x << " ";
    }
    cout << endl;

    return 0;
}

Output:

v2: 10 10 10 10 10

3. Adding and Removing Elements

The vector class provides functions to add or remove elements dynamically.

Adding Elements:

vector<int> v;
v.push_back(1); // Adds 1 to the end
v.push_back(2); // Adds 2 to the end

cout << "Elements: ";
for (int x : v) {
    cout << x << " ";
}

Removing Elements:

v.pop_back(); // Removes the last element
cout << "\nAfter pop_back: ";
for (int x : v) {
    cout << x << " ";
}

Output:

Elements: 1 2 
After pop_back: 1

4. Accessing Elements

You can access elements using:

  1. Subscript Operator ([]):
    vector<int> v = {10, 20, 30}; cout << "First element: " << v[0] << endl;
  2. at() Method:
    cout << "Second element: " << v.at(1) << endl;
  3. Front and Back:
    cout << "First: " << v.front() << ", Last: " << v.back() << endl;

Output:

First element: 10
Second element: 20
First: 10, Last: 30

5. Iterating Through a vector

Using a for Loop:

vector<int> v = {1, 2, 3};
for (int i = 0; i < v.size(); i++) {
    cout << v[i] << " ";
}

Using a Range-Based for Loop:

for (int x : v) {
    cout << x << " ";
}

Using Iterators:

for (auto it = v.begin(); it != v.end(); ++it) {
    cout << *it << " ";
}

Output:

1 2 3

6. Common Operations

Check Size and Capacity:

cout << "Size: " << v.size() << ", Capacity: " << v.capacity() << endl;

Resize the Vector:

v.resize(5, 0); // Resize to 5 elements, new elements initialized to 0

Clear the Vector:

v.clear(); // Removes all elements
cout << "Size after clear: " << v.size() << endl;

Check if Empty:

if (v.empty()) {
    cout << "Vector is empty.\n";
}

7. Sorting a vector

You can sort a vector using sort() from <algorithm>:

#include <algorithm> // Required for sort()

vector<int> v = {3, 1, 4, 1, 5};
sort(v.begin(), v.end()); // Sort in ascending order

cout << "Sorted vector: ";
for (int x : v) {
    cout << x << " ";
}

Output:

Sorted vector: 1 1 3 4 5

8. Advanced Usage

Using a Vector of Pairs:

vector<pair<int, string>> students = {{1, "Alice"}, {2, "Bob"}};
for (const auto& student : students) {
    cout << "ID: " << student.first << ", Name: " << student.second << endl;
}

Nested Vectors:

vector<vector<int>> matrix = {{1, 2}, {3, 4}, {5, 6}};
for (const auto& row : matrix) {
    for (int x : row) {
        cout << x << " ";
    }
    cout << endl;
}

Summary

  • vector is a versatile and efficient container for managing dynamic arrays in C++.
  • It offers dynamic sizing, random access, and a rich set of functions for easy manipulation.
  • Combine it with other STL components (like sort) for powerful data manipulation.

With these basics, you can effectively use vector in a wide range of C++ applications!

Scroll to Top