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Track with Vectors

Explore how to use dynamic vectors in C++ to manage flexible data lists. Learn to create, add, remove, and access elements, compare vectors with arrays, and iterate through vectors using loops to build smarter, adaptable code.

We'll cover the following...

You’ve used fixed-size arrays. Now let’s upgrade to dynamic containers: vector. Vectors let you add, remove, and manage data on the fly.

Vector with indices
Vector with indices

Goal

You’ll aim to:

  • Use vector to store flexible lists.

  • Add, access, and loop through items.

  • Compare with arrays.

Include the vector library

#include <vector>

 Always include it at the top.

Create and initialize a vector

We can create a vector in C++ and initialize it with starting values. After that, we can still add more elements when needed.

C++
#include <iostream>
#include <vector>       // For using the vector container
using namespace std;
int main() {
    vector<int> numbers = {1, 2, 3};   // Declares a vector and initializes it with 3 integers
    numbers.push_back(4);  // Adds 4 to the end of the vector
    cout << numbers[3] << endl;   // Prints the 4th element in the vector (index 3)
    return 0;
}

push_back() adds elements dynamically.

Updating a vector with push.back ( )
Updating a vector with push.back ( )

Iterate through a vector

Let’s iterate through a vector in C++ using a for loop and indexing, and see how the vector looks before and after we update it using push_back():

C++
#include <iostream>
#include <vector>
using namespace std;
int main() {
    vector<int> numbers = {1, 2, 3};
    cout << "Vector (before push_back()): ";
    for (int i = 0; i < numbers.size(); i++) {     // Loops through the vector using its size
      cout << numbers[i] << " ";       // Prints each number in the vector before push.back()
    }
    
    numbers.push_back(4);  // Add item
    cout << endl << "Vector (after push_back()): ";
    for (int i = 0; i < numbers.size(); i++) {     // Loops through the vector using its size
      cout << numbers[i] << " ";       // Prints each number in the vector after push.back()
    }
    return 0;
}

You’ve looped through dynamic data.

This is one common way to iterate through a vector using a traditional for loop and indexing.

Vector features

  • Grows and shrinks automatically.

  • .size() returns the current length.

  • push_back(), pop_back() = add/remove