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Vectors

Vector Type

Adding or Removing Elements

.size() Vector Function

Index

Vectors

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

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.

All the elements are stored in contiguous locations, which means that they can be accessed with an index. The first index in a vector is 0.

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

Vector Type

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

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.

Adding or Removing Elements

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

In C++, 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

.size() Vector Function

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

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

Index

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

In C++, an index refers to an element’s position within an ordered list, like a vector or an array.

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

Note: The first element in a vector or an array has an index of 0.

Vectors
Lesson 1 of 1
  1. 1
    To do just about anything of interest in a program, we need a group of data to work with. For example, our program might need: - A list of Twitter’s trending tags - A set of payment options for a…
  2. 2
    The std::vector lives in the header. So first, we need to add this line of code at the top of the program: #include For review, #include is a preprocessor directive that tells the compiler t…
  3. 3
    Now we know how to create a vector, we can also initialize a vector, giving it values, as we are creating it in the same line. For example, instead of just creating a double vector named location:…
  4. 4
    Now that we have a vector, how do we access an individual element? This is where index comes into play. An index refers to an element’s position within an ordered list. Vectors are 0-indexed, me…
  5. 5
    Often, we start with a vector that’s either empty or a certain length. As we read or compute data we want, we can grow the vector as needed. ##### .push_back() ##### To add a new element to the “…
  6. 6
    not only stores the elements; it also stores the size of the vector: size The .size() function returns the num…
  7. 7
    So what happens when you want to change each of the values within a vector? You can use a for loop! For example, suppose we have an int vector that looks like this: ![1](https://codecademy-conte…
  8. 8
    Congratulations! You have learned about how to store groups of data into vectors in C++.  Here are some of the things that we learned: - Vectors are a sequence of elements that you can access by…

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