// mediangrades.cpp

#include <algorithm>
#include <cmath>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <vector>
using namespace std;

void
read_grades( vector<int> &grades, ifstream &grade_stream )
{
  int grade;
  while ( grade_stream >> grade )
  {
    grades.push_back( grade );
  }
}

      // (we're passing grades by reference to avoid a COPY)
void                     // const means grades cannot change
compute_avg_and_std_dev( const vector<int> &grades,
                         double &avg, double &std_dev )
{
  // Compute the average
  int sum=0;
  for ( unsigned int i = 0; i < grades.size(); i++ )
  {
    sum += grades[i];
  }
  avg = double(sum) / grades.size();

  // Compute the standard deviation
  double sum_sq = 0.0;
  for ( unsigned int i = 0; i < grades.size(); i++ )
  {
    sum_sq += ( grades[i] - avg ) * ( grades[i] - avg );
  }
  std_dev = sqrt( sum_sq / ( grades.size() - 1 ) );
}

double
compute_median( const vector<int> &grades )
//compute_median( vector<int> grades )
{
  // Create a copy of the vector
  vector<int> grades_to_sort( grades );

  // Sort the values in the vector (default is increasing order)
  sort( grades_to_sort.begin(), grades_to_sort.end() );

  // Compute median
  unsigned int n = grades_to_sort.size();

  if ( n % 2 == 0 ) // even number of grades
    return double( grades_to_sort[ n / 2 ] + grades_to_sort[ n / 2 - 1] ) / 2.0;
  else
    return double( grades_to_sort[ n / 2 ] );
}

int
main( int argc, char* argv[] )
{
  cout << "argc is " << argc << endl;

  if ( argc != 2 )
  {
    cerr << "Usage: " << argv[0] << " <grades-file>\n";
    return 1;
  }

  // Open the grades.txt file (i.e. argv[1])
  //   (bail if an error occurs)
  ifstream grades_stream( argv[1] );
  if ( !grades_stream )
  {
    cerr << "Cannot open grades file " << argv[1] << endl;
    return 1;
  }

  vector<int> grades;
  read_grades( grades, grades_stream );

  // Quit with an error message if no grades loaded
  if ( grades.size() == 0 )
  {
    cout << "No grades entered." << endl;
    return 1;
  }

  // Compute average, standard deviation, and median
  double average, std_dev;
  compute_avg_and_std_dev( grades, average, std_dev );
  double median = compute_median( grades );

  cout << "From " << grades.size() << " grades: \n"
       << "  average is " << setprecision(3) << average << '\n'
       << "  std_dev is " << std_dev << '\n'
       << "   median is " << median << endl;

  return 0;  //  Everything ok
}