#include <algorithm>
#include <iostream>

int main()
{
  double arr[] = { 1, 2, 3, 3, 4 };
  double *ptr = std::adjacent_find(arr, arr+5);
  if (ptr != end(arr))
  {
    std::cout << ptr[0] << " == " << ptr[1] << '\n';
  }
}