declare vector of size n in c++

// First include the vector library:
#include <vector>

// The syntax to create a vector looks like this:
std::vector<type> name;

// We can create & initialize "lol" vector with specific values:
std::vector<double> lol = {66.666, -420.69};

// it would look like this: 66.666 | -420.69

#include <vector>

int main() {
  std::vector<int> myVector = { 666, 1337, 420 };
  
  size_t size = myVector.size(); // 3
  
  myVector.push_back(399); // Add 399 to the end of the vector
  
  size = myVector.size(); // 4
}

// CPP program to initialize a vector like 
// an array. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vect{ 10, 20, 30 }; 
  
    for (int x : vect) 
        cout << x << " "; 
  
    return 0; 
} 

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

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

#include <vector>

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