#include <iostream.h>

#include "TFile.h"
#include "TTree.h"
#include "TRandom.h"
#include "TROOT.h"

extern void InitGui();
VoidFuncPtr_t initfuncs[] = {InitGui, 0};
TROOT root("Rint","The ROOT Interactive Interface", initfuncs);


int main() {

   // -- Open a TFile 
   TFile *f = new TFile("SimpleTree.root","recreate");

   // -- for each event, you want up to 500 candidates (or whatever)
   Int_t n;          // keeps track of how many per event
   Double_t E[500];
   Float_t  Px[500];
   Float_t  Py[500];
   Float_t  Pz[500];

   // -- Instantiate a tree
   TTree* pMyTree = new TTree("SimpleTree","An example of a tree");

   // -- Define branches  (Note: that the second argument is a pointer)
   pMyTree->Branch("n",&n,"n/I");      // I is integer
   pMyTree->Branch("E",E,"E[n]/D");    // D is double
   pMyTree->Branch("Px",Px,"Px[n]/F"); // F is float
   pMyTree->Branch("Py",Py,"Py[n]/F");
   pMyTree->Branch("Pz",Pz,"Pz[n]/F");

   // -- Run over 100 'events' 
   for (Int_t i=0; i<100; i++) {
     n = 500*gRandom->Rndm();       // each event has a random number of candidates
     for (Int_t j=0; j<n; j++) {
       E[j] = gRandom->Gaus(10., 2.);
       Px[j] = gRandom->Gaus(5, 1.);
       Py[j] = gRandom->Gaus(5., 1.);
       Pz[j] = gRandom->Gaus(7., 0.6);
     }
     // -- Fill the tree 
     pMyTree->Fill();
   }

// -- Show what we got
pMyTree->Print();

// -- Dump it to a file
pMyTree->Write();

// -- And clean up
f->Close();
delete f;
}