using namespace std;

void Normalize(TH1F* hist)
{
// Normalizes a 1-d histogram to its bin width and number of events
  if (hist->GetSumw2N() == 0) hist->Sumw2(kTRUE);//hist->Sumw2();
  hist->Scale(1.0 / hist->Integral(),"width");
}

void PlotsN()
{
gSystem->cd("/home/saumyen/Desktop/Histograms");

const char *inputFile0 = "/home/saumyen/Desktop/Histograms/ttjj.root";
const char *inputFile1 = "/home/saumyen/Desktop/Histograms/twjj.root";
std::vector<const char *> inputFiles = {inputFile0, inputFile1};
Int_t ii = inputFiles.size();

  //Booking the Canvases
   TCanvas *c1 = new TCanvas("LeadM","Leading Jet Mass",800,600);
   TCanvas *c2 = new TCanvas("SubleadM","Subleading Jet Mass",800,600);
   TCanvas *c[2] = {c1,c2};

  //Booking the Stacks
   THStack *M0 = new THStack("h7","");
   THStack *M1 = new THStack("h8","");
   THStack *Stacks[2] = {M0, M1};

//Booking the Histograms
TH1F *histM0[ii], *histM1[ii];

for(Int_t f=0; f<ii; f++)
{
  TFile *infile = new TFile(inputFiles[f], "read");
  TTree *event_tree = (TTree*)infile->Get("event");
int entries = event_tree->GetEntries();
cout<<entries<<endl;

// Variable initialization
Double_t jetM0(0), jetM1(0);

event_tree->SetBranchAddress("var7",&jetM0);
event_tree->SetBranchAddress("var8",&jetM1);


   histM0[f] = new TH1F(Form("J0_Mass%d",f), "J0 Mass", 40, 0.0, 200.0);
   histM1[f] = new TH1F(Form("J1_Mass%d",f), "J1 Mass", 40, 0.0, 200.0);

   std::vector<TH1F *> histos = {histM0[f], histM1[f]};
   int hh = histos.size();

for(int i = 0; i < entries; i++)
{
event_tree->GetEntry(i);
//cout<< jetM0 << "\t" << jetM1<<endl;

      histM0[f] -> Fill(jetM0); 
      histM1[f] -> Fill(jetM1); 
}

for(int h=0; h<hh; h++)
{
histos[h]->SetLineColor(2);
Normalize(histos[h]);
Stacks[h] -> Add(histos[h]);
}

infile->Close();
}

for(int j=0; j<2; j++)
{
c[j]->cd();
Stacks[j]->Draw("hist nostack");

c[j]->Modified(); c[j]->Update();
TString fname(c[j]->GetName()); fname += TString::Format(".png");
c[j]->Print(fname,"png");
}

} //main function