#include <numeric>
#include <iostream>

int main()
{
  double a[] = { 2, 4, 6, 8 };
  double b[] = { 2, 3, 5, 7 };

  std::cout << "Skalarprodukt      = " 
               // 4+12+30+56 = 102 
            << std::inner_product(a, a+4, b, 0.0) << '\n';

  std::cout << "Produkt der Summen = " 
               // 4*7*11*15 = 462
            << std::inner_product(a, a+4, b, 0.0,
                 std::multiplies{}, std::plus{}) << '\n';
}