#include <TRandom2.h>

// histograms filled and drawn in a loop
void krogint() {

  TCanvas *c1 = new TCanvas("c1","Primer MC integracije",200,10,600,600);
  c1->SetGrid();


// Create some histograms.
  main   = new TF1("krog","sqrt(1.-x*x)",0.,1.);
  main->SetFillColor(41);
 
  //random
  TRandom *rand = new TRandom2();


// Fill histograms randomly
  rand->SetSeed(4434333);
  const Int_t niter=1000000;
  gr = new TGraph(niter);
  gr2 = new TGraph(niter);
  Double_t xsum=0.;
  Double_t xtot=0.;
  Double_t x=0.;
  Double_t y=0.;
  for ( Int_t  i=0; i<niter; i++) {
    Double_t r1 = rand->Rndm();
    Double_t r2 = rand->Rndm();
    x=r1;
    y=r2;
    //std::cout << x << ' ' << y << std::endl;
    if ( x*x+y*y <= 1.0000) {
      gr->SetPoint(i,x,y);
      xsum++;
    }
    else{
      gr2->SetPoint(i,x,y);      
    }
    xtot++;
    //main->Fill(xmain);
  }

  main->Draw();

  //point overlay
  //gr = new TGraph(niter,xa,ya);
  gr->SetLineColor(1);
  gr->SetLineWidth(1);
  gr->SetMarkerColor(4);
  gr->SetMarkerStyle(21);
  gr->Draw("P");
  gr2->SetLineColor(1);
  gr2->SetLineWidth(1);
  gr2->SetMarkerColor(2);
  gr2->SetMarkerStyle(21);
  gr2->Draw("P");

  Double_t xres=xsum/xtot*4.;
  Double_t pi=TMath::Pi();
  std::cout << "rezultat=" << xres << " rel=" << 1-xres/pi << " pi=" << pi << std::endl;

  c1->Update();
  c1->Modified();
}