// Reading data from a file with a check for is_open()
#include <iostream>
#include <fstream>
using namespace std;

int main ()
{
  string filename = "kelvin.tmp";
  ifstream kelvin(filename.c_str());
  double k;

  if (kelvin.is_open())
  {
      double s;
      int i;

      cout << "Reading data from file: " << filename << endl;
      for(s = 0.0, i=0; i<100; i++, s += k )
         kelvin >> k;
      kelvin.close();

      double mean = s/100.0;

      cout << "mean of the data = " << mean << endl;
  }
  else
    cout << "Unable to open file " << filename;

  return 0;
}