// A program that illustrate the difference between the plus operator
// and a function of two arguments that adds the arguments together.

#include <iostream>
#include <list>
#include <numeric>     // accumulate
#include <functional>  // plus

int main(){
  using namespace std;

  // We make a list of doubles, and insert some numbers in the list:
  list<double> lst;
  for(int i = 1; i <= 10; i++) lst.push_back(i);   // 1, 2, ..., 10

  // An operator is NOT a first class entity in C++:
  double res = accumulate(lst.begin(), lst.end(), 0.0, + );   // error: expected primary-expression ....

  // We must make an object which serves as a binary plus function: 
  double res = accumulate(lst.begin(), lst.end(), 0.0, plus<double>{});

  cout << "The plus accumulation is: " << res << endl;       // 55
}