how to take size of array from user in c++ code example

Example: how to get size of array c++

How do I find the length of an array?
//Method 1:
- use sizeof(arr)/sizeof(*arr) 

//Method 2: 
- use std::array from  C++11
array <int,6> arr{1, 2, 3, 4, 5, 6}; 
cout << arr.size();