/* This program reads a stream of int values and prints the sum.
 * The loop is in the copy algorithm which can copy to any object
 * with operator* and operator++ methods.
 * The summation object is behaving like an iterator.
 * Because the summation object is copied the instance variables
 * sum and next need to be outside the object :(.
 */
#include <iostream>
#include <algorithm>  // copy
#include <iterator> 
 template <class T>
 class summation { T &sum, &next;
  public:
   summation(T& ps, T& pn):sum(ps), next(pn) {}
   T & operator* (){ return next; } // will be assigned next input value
   summation& operator++ () { sum += next; return *this;}
 };
int main() {  
 int next, sum=0;  // used by summation
 std::istream_iterator<int>first(std::cin),  last;
 std::copy(first, last, summation<int>(sum, next) );
 std::cout << sum << "\n";
}