void prova()
{
   Int_t n = 10;
   Float_t arr[n];

   TFile fout("output.root","RECREATE");

   TTree *tree = new TTree("tree","example for array");
   tree->Branch("n",&n,"n/I");
   tree->Branch("arr",arr,"arr[n]/F");

   for (int k=0; k<n; k++) {
      double val = gRandom->Uniform(0,1);
      arr[k]=val;
   }

   cout<<"Array done\n";

   tree->Fill();

   cout<<"Tree Filled\n";

   fout.cd();
   fout.Write();
   fout.Close();

   cout<<"File Ready\n";
}