#include <iostream>
#include <fstream>

using namespace std;

void writeReadDataGraph(const int num=1000) {
  // write data to file
  //ofstream ofile("data",ios::binary);
  ofstream ofile("data");
  for (int i=0; i<num; ++i){
    float rnd = gRandom->Rndm();
    float err = gRandom->Rndm()*10.;
    //cout << "rnd " << rnd << endl;
    float y = 10.*i+5.+rnd*10.;
    //cout << "rnd " << rnd << " i " << i << " y " << y << endl;
    ofile << i*1. << " " << y << " " <<  err << endl;
  }
  ofile.close();

  // now read data from file
  //ifstream ifile("data",ios::binary);
  ifstream ifile("data");
  int nlines=0;
  float xx[num];
  float exx[num];
  float yy[num];
  float eyy[num];
  while (ifile.good()) {
    float x,y,ey;
    ifile >> x >> y >> ey;
    //cout << "Entry:" << nlines << ": X " << x << " Y " << y << endl;
    if (ifile.eof()) break;
    xx[nlines]=x;
    yy[nlines]=y;
    exx[nlines]=0.1;
    eyy[nlines]=ey;
    nlines++;
  };
  ifile.close();
  gStyle->SetOptFit(1111);
  gr1 = new TGraphErrors(nlines,xx,yy,exx,eyy);
  gr1->SetMarkerColor(kBlue);
  gr1->SetMarkerStyle(21);
  gr1->Fit("pol1");
  TF1* f=dynamic_cast<TF1*>(gr1->GetFunction("pol1"));
  cout << "F: " << f->GetChisquare() << " NDoF " << f->GetNumberFreeParameters()<< " " << f->GetNumberFitPoints() << endl;
  gr1->Draw("ALP");
}