//
// like ave.cpp, but redesigned to allow alternative streams
//

#include <iostream>
#include <sstream>
#include <cassert>
#include <cmath>                // for fabs
#include <iomanip>              // for setprecision

using namespace std;

const double EPSILON = 1e-6;

// return average of double inputs as a double or 0.0 if there are no inputs
//
// note the istream is passed by reference
//
double average(istream& input) {
   double sum = 0.0;
   double number;
   int count = 0;
   input >> number;
   while ( input ) {
      sum += number;
      ++count;
      input >> number;
   }
   return count == 0 ? 0.0 : sum / count;
}

// report average to three significant places
//    (written as a separate function to illustrate output streams)
//
// again, note the ostream is passed by reference
//
void report_average(ostream& output, double value) {
   output << "Average: " << setprecision(3) << std::fixed << value;
}

int main() {
   { 
      // test the average function
      istringstream nums("5.5 7.0 10.0");
      double a = average(nums);
      assert(fabs(a - 7.5) < EPSILON);
      istringstream empty("    ");
      a = average(empty);
      assert(a == 0.0);         // comparing to 0 IS safe

      // test the full input/output; reusing nums just to illustrate
      //   how to update a string stream to a new value
      nums.clear();
      nums.str("101 81 93 453 18 515");
      ostringstream test_output;
      report_average(test_output, average(nums));
      assert(test_output.str() == "Average: 210.167");
   }
   cout << "Enter numbers (using end-of-file at end): ";
   double ave = average(cin);
   report_average(cout, ave);
   cout << endl;
   return 0;
}