void macro5()
{
  // creazione di un istogramma

  TH1F *h1 = new TH1F("h1","x1",1000,0,100);
  h1->SetLineColor(2);

  TH1F *h2 = new TH1F("h2","x2",1000,0,100);
  h2->SetLineColor(4);

  TH1F *h = new TH1F("h","x1+x2",1000,0,100);

  for (int i=0; i<1000000; i++) {

    // grandezza x = 20.0 +- 1.0
    double x1 = 19 + gRandom->Rndm()*2;
    h1->Fill(x1);

    // grandezza x = 30.0 +- 2.0
    double x2 = 28 + gRandom->Rndm()*4;
    h2->Fill(x2);

    double x = x1+x2;
    h->Fill(x);
  }
  
  h1->Draw();
  h2->Draw("same");
  h->Draw("same");

}