void drawHistos() {

  //aprire il file di istogrammi 
  
  TFile * file = new TFile("histo.root","old");
  file->ls(); 
  TH1F* h1 = (TH1F*)file->Get("s1");
  TH1F* h2 = (TH1F*)file->Get("s2");
  TH1F* htotal = (TH1F*)file->Get("total");
  TH1F* hmain = (TH1F*)file->Get("main");
  
  
  //estraggo media, RMS e integrale dell'istogramma s1
  
  Float_t integral=h1->Integral();
  Float_t mean =h1->GetMean();
  Float_t rms =h1->GetRMS();
  
  cout << " integrale h1 = " << integral << " mean = " << mean << " RMS = " << rms << endl;
  

  TCanvas *c1 = new TCanvas("c1","Histogram Example",200,10,600,400);
  c1->SetGrid();

//drawing degli istogrammi

  htotal->Draw("ep");
  hmain->Draw("same");
  h1->Draw("same");
  h2->Draw("same");

  c1->Print("myhistos.pdf");
  c1->Print("myhistos.root");
  c1->Print("myhistos.C");
 
  //operazioni su istogrammi
  TCanvas *c2 = new TCanvas("c2","Histogram Example",200,10,600,400);
  c1->SetGrid();

  TH1F *mytotal = new TH1F(*hmain);
  mytotal->SetName("mytotal2");
  mytotal->SetFillColor(0);
  mytotal->Add(h1,1.);
  mytotal->Add(h2,1.);
  mytotal->Draw("hist");
  mytotal2->Draw();
 //  file->ls();
 // file->Close();

}