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Vectors

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Vectors

In C++, a vector is a dynamic list of items, that can shrink and grow in size. It is created using std::vector<type> name; and it can only store values of the same type.

To use vectors, it is necessary to #include the vector library.

#include <iostream> #include <vector> int main() { std::vector<int> grades(3); grades[0] = 90; grades[1] = 86; grades[2] = 98; }

Vector Type

During the creation of a C++ vector, the data type of its elements must be specified. Once the vector is created, the type cannot be changed.

.push_back() & .pop_back()

The following functions can be used to add and remove an element in a vector:

  • .push_back() to add an element to the “end” of a vector
  • .pop_back() to remove an element from the “end” of a vector
std::vector<std::string> wishlist; wishlist.push_back("Oculus"); wishlist.push_back("Telecaster"); wishlist.pop_back(); std::cout << wishlist.size(); // Prints: 1

.size() Function

The .size() function can be used to return the number of elements in a vector, like name.size().

std::vector<std::string> employees; employees.push_back("michael"); employees.push_back("jim"); employees.push_back("pam"); employees.push_back("dwight"); std::cout << employees.size(); // Prints: 4

Index

An index refers to an element’s position within an ordered list, like a vector or an array. The first element has an index of 0.

A specific element in a vector or an array can be accessed using its index, like name[index].

std::vector<double> order = {3.99, 12.99, 2.49}; // What's the first element? std::cout << order[0]; // What's the last element? std::cout << order[2];