#include "TH1.h"
#include "TF1.h"
#include "Riostream.h"
void hist() {
  ifstream in;
  in.open("eu_gu_1.txt"); 
  Int_t i, npeaks = 5;
  auto f = TFile::Open("hist.root","RECREATE"); 
  TCanvas *c1 = new TCanvas("c1","c1");
  TGraph *g = new TGraph("eu_gu_1.txt");
  // g->Sort(); // just a precaution
  Int_t n = g->GetN();//get the no. of points on the TGraph *g
  Double_t source[n];
  Double_t *x = new Double_t[(n + 1)];
  x[0] = (3.0 * g->GetX()[0] - g->GetX()[1]) / 2.0;
  x[n] = (3.0 * g->GetX()[(n - 1)] - g->GetX()[(n - 2)]) / 2.0;
  for (Int_t i = 1; i < n; i++)
    { x[i] = (g->GetX()[(i - 1)] + g->GetX()[i]) / 2.0; }
  TH1D *h1 = new TH1D("h1", "spectrum;x-value(Channels);#counts", n, x);
  
  h1->FillN(n, g->GetX(), g->GetY());
  h1->Sumw2(kFALSE); // restore proper errors
  delete [] x; // no longer needed
  delete g; // no longer needed
  h1->Draw();
  in.close();
  f->Write();

}