Find the number from an array which is not repeated twice. C++

Here is the Code :

#include <iostream>
#include <conio.h>

using namespace std;

void main()
{
  int arr[] = { 1, 2, 3, 4, 5, 6, 6, 7, 8, 7, 8, 1, 4, 2,3 };
  int result = 0;
  int len = sizeof(arr) / sizeof(int);

  for (int index = 0; index < len; ++index)
  {
    result ^= arr[index];
  }
  
  cout << result;

  _getch();
}

Thanks