Vectors in C++

std::vector are usually not called vectors, often array links or dynamic arrays. Usually, you do not to provide a length to the vector - you can add elements and it will resize under the hood, as inside of the container a new array is created on each resize.

First of all, you need to include the container:

#include <vector>

Creating a vector

std::vector<int> numbers;

Primitive types can be passed to the vector as the type.

Adding data to the vector:

numbers.push_back(1);
numbers.push_back(2);

Iterating over the vector:

one can iterate over it with an for loop, as we can get the number of the elements in the vector:

for (int i = 0; i < numbers.size(); i++)
  cout << numbers[i] << endl;

// or:

for (int number : numbers)
  cout << number << endl;

Cleaning the whole vector:

numbers.clear();

Returning a vector

vector<int> returnVector() {
  vector<int> values;

  return values;
}

With assigning the value to another vector:

vector<int> returnNumbers() {
  vector<int> numbers;
  numbers.push_back(1);
  numbers.push_back(2);

  return numbers;
};

int main() {
  vector<int> newNumbers = returnNumbers();

  cout << newNumbers[0] << endl;
  // prints "1"
  return 0;
}

Passing a vector to a function

There are two ways to do so:

1. Passing by value
2. Passing by reference

When passing by value, inside of the recievings function scope, a copy is created:

void printFirstNumber(vector<int> numbers) {
  cout << numbers[0] << endl;
};

int main() {

  vector<int> numbers;

  numbers.push_back(1);
  numbers.push_back(2);
  numbers.push_back(3);

  printFirstNumber(numbers);

  return 0;
}

When passing by reference, we can mutate the original state:

void changeFirstNumber(vector<int> &numbers) {
  numbers[0] = 2;
};

int main() {
  // vector<int> numbers;
  vector<int> numbers;
  numbers.push_back(1);

  changeFirstNumber(numbers);

  cout << numbers[0] << endl;
  // prints "2"

  return 0;
}

Vector of arrays

A vector, as a not-fixed structure in size can hold multiple arrays and therefore act as an flexible two-dimensional array alternative. Coming soon.

Loop over a vector

vector<int> numbers;

numbers.push_back(1);
numbers.push_back(2);
numbers.push_back(3);

for (int number : numbers) {
  cout << number << endl;
}