how to get size of array c 2b 2b

1int arr[5];
2int len = sizeof(arr) / sizeof(arr[0]);
3// returns 5

1int a[20];
2int length;
3length = sizeof(a) / sizeof(int);
4

1#include <iostream>
2using namespace std;
3
4#define size(type) ((char *)(&type+1)-(char*)(&type))
5
6int main(){
7  int arr[5] = {1, 2, 3, 4, 5};
8  cout << size(arr) / size(arr[0]) << endl; //returns 5
9  //alternatively
10  cout << sizeof(arr) / sizeof(int) << endl; //returns 5
11}

1#include <iostream>
2using namespace std;
3int main() {
4   int arr[5] = {4, 1, 8, 2, 9};
5   int len = sizeof(arr)/sizeof(arr[0]);
6   cout << "The length of the array is: " << len;
7   return 0;
8}

1int size = sizeof(arr)/sizeof(arr[0])

1How do I find the length of an array?
2//Method 1:
3- use sizeof(arr)/sizeof(*arr) 
4
5//Method 2: 
6- use std::array from  C++11
7array <int,6> arr{1, 2, 3, 4, 5, 6}; 
8cout << arr.size();