#include <iostream>
#include <vector>

#include "TFile.h"
#include "TTree.h"

using namespace std;

int main(){

  TFile fDB("./testW.root","recreate","demo file");
  TTree* t=new TTree("t","tree DB");

  vector<float> a;

  t->Branch("a", &a, "a");
  
  for (int i=1; i<3; i++){ 
    a.push_back(float(i));
  }

  for (int i=0; i<2; i++){ 
    cout<<"a["<<i<<"]="<<a.at(i)<<endl;;
  }


  t->Fill();          
    
  fDB.Write();
  fDB.Close();
  
  return 0;
}