C++ Vectors

Creating a vector

Include the <vector> header, then declare a vector by naming the type of data it will hold inside angle brackets. You can start it empty or fill it with values right away using curly braces.

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

int main() {
  vector<string> fruits = {"apple", "banana", "cherry"};

  cout << fruits[0] << "\n";
  cout << fruits[1] << "\n";
  cout << fruits[2] << "\n";
  return 0;
}

Adding and removing elements

Use push_back() to add an element to the end of a vector, and pop_back() to remove the last element. This ability to change size while running is what makes vectors more flexible than plain arrays.

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

int main() {
  vector<string> colors;
  colors.push_back("red");
  colors.push_back("green");
  colors.push_back("blue");

  colors.pop_back(); // removes "blue"

  cout << "There are " << colors.size() << " colors left.";
  return 0;
}

Common vector functions

Vectors come with helpful built-in functions. Here are the ones you will reach for most often as a beginner.

Looping through a vector

The cleanest way to visit every element is a range-based for loop. It reads each element one by one without you needing to manage index numbers. Using the & symbol with auto avoids copying each element.

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

int main() {
  vector<int> scores = {90, 75, 88, 100};
  int total = 0;

  for (const auto& score : scores) {
    total += score;
  }

  cout << "Total score: " << total;
  return 0;
}

• A vector can grow and shrink while the program runs.
• Include <vector> and declare the element type in angle brackets.
• Add with push_back() and remove with pop_back().
• Use size() to count elements and a range-based for loop to visit them.