how to initialize size of vector in c++ code example

Example 1: how to initialize vector

vector<int> vect{ 10, 20, 30 };

Example 2: c++ create vector of size

// create a vector with 20 integer elements
std::vector<int> arr(20);

for(int x = 0; x < 20; ++x)
   arr[x] = x;

Example 3: declare vector of size n in c++

#include <vector>

auto n = 20
// create a vector with n=20 integer elements
std::vector<int> arr(n);