# Vector size() function in C++

Hi folks! In this tutorial we are going to learn and focus on what are vectors and about a special function associated with vectors ie. vector size().

What are vectors?

They are dynamic arrays that can resize themselves whenever an element is inserted or deleted from it.

## vector size() function

vector::size function is a function associated with vectors. This function allows you to find the number of elements in a vector. In short, we can say it returns the size of the vector.

There are no parameters required in the size function. vector size() function returns an integer value . Time complexity is big o(1).

syntax:- `vector_name.size()`

Let’s understand this function using a code as an example:

## C++ Code: vector size()

```#include<iostream>
#include<vector>
using namespace std;
int main()
{
// declare name of variable as num
vector<int>num;
// insert 5 numbers using push_back function
num.push_back(3);
num.push_back(5);
num.push_back(7);
num.push_back(9);
num.push_back(11);
cout<<num.size();
return 0;

}```

Output:

`5`

## Explanation of the code

The code written above demonstrates the example of size() function. First, declare the name of the vector. Then using push_back() we will insert the elements in the vector, 5 elements are inserted and the size function() will return an integer value which indicates the size of the vector as output.