{
//
// Determine Pi by integration of a circle with random numbers
// 

gROOT->Reset();

  float	  pi=0.0;
  int	  Nac=0,Ntot=0;
  TCanvas *c1;
  TPad    *pad,*padtx;

  number_of_points=100000;

//  create canvas
  c1 = new TCanvas("cpi","Calculate Pi",200,10,400,600);
  c1->SetGrid();
  c1->SetFillColor(42);

// create random object
  TRandom *myRnd=new TRandom();

// pad for text and plot
  padtx = new TPad("pad2","Pad for value of Pi",0.02,0.82,0.98,0.98,21);
  padtx->Draw();
  pad = new TPad("pad1","Pad for 2D Plot",0.02,0.02,0.98,0.8,21);
  pad->Draw();
  padtx->cd();
  char text[50];
  sprintf(text,"Pi = %f",pi);
  TText* Pitxt=new TText(0.1,0.1,text);
  Pitxt->SetTextSize(0.6);
  Pitxt->Draw();  
// create 2d-Histo
  pad->cd();
  TH2F* h2fac = new TH2F("h2fPiac","Circle accepted random numbers",100,0.0,1.0,100,0.,1.);
  h2fac->SetMarkerStyle(21);
  h2fac->SetMarkerSize(0.2);
  h2fac->SetMarkerColor(2);
  h2fac->SetFillColor(2);
  TH2F* h2frej = new TH2F("h2fPirej","Rejected random numbers",100,0.0,1.0,100,0.,1.);
  h2frej->SetMarkerStyle(21);
  h2frej->SetMarkerSize(0.3);
  h2frej->SetMarkerColor(3);
  h2frej->SetFillColor(3);
  float x1,x2;
  for(int i=1;i<number_of_points;++i) {
    x1 = myRnd->Rndm();
    x2 = myRnd->Rndm();
    Ntot++;
    if(sqrt(x1*x1+x2*x2) <= 1.0) 
      {
	Nac++;
	h2fac->Fill(x1,x2);
      }
    else
      {
	h2frej->Fill(x1,x2);
      }
    
    if(i%1000 == 0) {
      pad->cd();
      h2fac->Draw();
      h2frej->Draw("same");
      if(Ntot > 0) pi = (float)Nac/(float)Ntot*4.0;
      sprintf(text,"Pi = %f",pi);
      padtx->cd();
      Pitxt->SetText(0.1,0.1,text);
      Pitxt->Draw();
      c1->Modified();
      c1->Update();
    }  
  }
  pad->cd();
  h2fac->Draw();
  h2frej->Draw("same");
  if(Ntot > 0) pi = (float)Nac/(float)Ntot*4.0;
  sprintf(text,"Pi = %f",pi);
  padtx->cd();
  Pitxt->SetText(0.1,0.1,text);
  Pitxt->Draw();
  c1->Modified();
  //  c1->Update();
}