Adding variables in a tree from different trees

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Hi Everyone !
I have two trees in my root file. The names are “dklfv”(variable inside D0_P4) & “pion”(variable name is pi_P4). I want to save these variables in a new tree. I have made an empty tree(nEmcPhotons). I want to save information in my newly made two branches(nPhot & mom). I am attaching the code I have written and the error I am getting. Please sort out the problem.
Thanks in Advance.

void ds()
  TFile *f = new TFile("peter.root", "recreate");
  float nPhot;
  float E[500];
  float mom;
    TTree* nEmcPhotons = new TTree("nEmcPhotons", "EMC Photons");
  nEmcPhotons->Branch("nPhot", &nPhot, "nPhot/F");
  nEmcPhotons->Branch("E", &E, "E[nPhot]/F");
  nEmcPhotons->Branch("mom", &mom, "mom/F");

  TFile* f2= new TFile("/home/souvik/root_work/lfv1.root");
  TTree* t2=(TTree*)f2->Get("dklfv");
  float pd3[4];
  t2->SetBranchAddress("D0_P4", &pd3);

  TH1F *hist2 = new TH1F("", " ", 50, 1.7, 2.1);

  Int_t n_tot2 = (int)t2->GetEntries();

  TLorentzVector v1(2.,2.,3.,4.);
  TVector3 p = v1.Vect();

  for (int i=0;i<100; i++)

      TLorentzVector D0_fvec(pd3);
      float fMomentum = D0_fvec.M();


  TFile* f1= new TFile("/home/souvik/root_work/lfv1.root");
  TTree* t1=(TTree*)f1->Get("pion");
  float pd1[4];
  t1->SetBranchAddress("pi_P4", &pd1);
  TH1F *hist1 = new TH1F("", " ", 50, 0.13956, 0.13958);
  TCanvas* c1 = new TCanvas();
  Int_t n_tot2_1 = (Int_t)t1->GetEntries();
  for (int i=0;i<n_tot2_1; i++)

      TLorentzVector D0_fvec(pd1);
      float fMomentum = D0_fvec.Mag();


error: member reference type 'float' is not a pointer
member reference type 'float' is not a pointer
nPhot = D0_fvec.M();
// ...
mom = D0_fvec.Mag();

Hi !
I tried with that comment after commenting out the lines nPhot->Fill(fMomentum); & mom->Fill(fMomentum);. The code is running but there is no entry in the root file. If I don’t comment out those lines I am getting the same error. Need help !

Hi !
I am waiting for your answer.

You never fill the output TTree!!!



to your loop …

humm worse, you never assign any value to any of the input variable nPhot, E nor mom …

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