c-resources/CPlusPlus20ForProgrammers-master/examples/ch06/fig06_12.cpp

// fig06_12.cpp
// Compute the product of an array's elements using accumulate.
#include <array>
#include <iostream>
#include <numeric>

template <typename T>
T multiply(T x, T y) {
   return x * y;
}


int multiply_int(int x, int y) {
   return x * y;
}


double f(double& x){
	return x*x;
}

template <typename T, typename F, long unsigned int N>
T integrate (std::array<T, N> x, F f){
	T tmp{T(0)};
	for (auto s: x){
            tmp+= f(s);
	}
	return tmp;
}


typedef double (*FUNC)(double&);


template <typename T, long unsigned int N>
T integrate2 (std::array<T, N> x, FUNC f){
        T tmp{T(0)};
        for (auto s: x){
            tmp+= f(s);
         }
         return tmp;
}


int main() {
   constexpr std::array integers{1, 2, 3, 4, 5};
   std::array floats {1.0, 2.0, 3.0, 4.0, 5.0};
   auto multiply_lambda = [](const auto& x, const auto& y) {return x * y; };

   auto f_lambda = [](auto& x) {return x*x;};

   auto g_lambda = [&integers](auto& x) {
	   auto tmp{0};
	   for (int i{0};auto s: x){
               tmp += s*integers[i];
	   }
	   return tmp;
   };

   std::cout << "Product of integers: " <<  std::accumulate( std::begin(integers), std::end(integers), 1, multiply<int>) << "\n";

   std::cout << "Product of integers: " <<  std::accumulate( integers.cbegin(), integers.cend(), 1, multiply<int>) << "\n";

   std::cout << "Product of integers with a lambda: " << std::accumulate(std::begin(integers), std::end(integers), 1, multiply_lambda) << "\n";

   std::cout << "Product of integers with a lambda: " << std::accumulate(std::begin(floats), std::end(floats), 1, multiply_int) << "\n";

   std::cout << "Product of integers with a lambda: " << std::accumulate(std::begin(floats), std::end(floats), 1, multiply_lambda) << "\n";

   std::cout << "Integration2  template  " << integrate2(floats, f) << "\n";

   std::cout << "Integration  full  template  " << integrate(floats, f_lambda) << "\n";

   std::cout << "Lambda test   " << g_lambda(floats) << "\n";
}


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