// rangauss.cxx : Fill Histogram with Gaussian Random numbers
//
#include <iostream>
#include <TH1.h>
#include <TCanvas.h>

int rangauss(const int Nrndm=2, const int Nfill=1000) 

{ 

// * define some constants
//const int Nrndm=2;   // fill one random number each time
//const int Nfill=1000; // number of times to fill histogram
const int Nbins=100;
const double xmin=-4.;
const double xmax=4;
const double pi=3.14159265359;

// normalised Gauss function
TF1 *gauss=new TF1("gauss","1/sqrt(2.*pi)*exp(-x*x/2.)",xmin,xmax);

// ----------------------------------------------------------------

// create main canvas
//                                        at xtop ytop sizex sizey
 TCanvas *theCanvas=new TCanvas("theCanvas","TestCanvas", 100, 100, 500, 600);
 TPad *txtPad = new TPad("txtPad","TextPad",0.,0.8,1.,1.);
 TPad *hstPad = new TPad("hstPad","HistPad",0.,0. ,1.,0.8.);
 txtPad->Draw();
 hstPad->Draw();

// set active pad to text pad and print some text
txtPad->cd();
gPad->SetFillColor(42); 
gStyle->SetTextColor(9);
TText* txtHead= new TText(0.1,0.7, "Gauß Distribution"); 
txtHead->SetTextSize(0.4);
txtHead->Draw();
char* txt[50];
sprintf(txt,"filling %i times with %i numbers",Nfill,Nrndm);
gStyle->SetTextColor(1);
TText* txtIntro= new TText(0.05,0.2, const_cast<char*>(txt)); 
txtIntro->SetTextSize(0.25);
txtIntro->Draw(); 

// set active pad to graphics pad 
hstPad->cd();
gPad->SetFillColor(0); 
gPad->SetGrid();
 
// some histogram style options
gStyle->SetHistLineColor(46); 
gStyle->SetHistFillColor(3);
gStyle->SetHistLineWidth(3);
gStyle->SetAxisColor(4,"X");
gStyle->SetAxisColor(4,"Y");
gStyle->SetLabelColor(4,"X");
gStyle->SetLabelColor(4,"Y");

// book a histogram, w. Nbins bins, range [xmin,xmax[
TH1F* hgauss =new TH1F("hgauss","Gauß distribution",Nbins,xmin,xmax);

// fill random numbers in a loop , Nfill times, Nrndm at a time
for(int j =0; j<Nfill; j++) {
 hgauss->FillRandom("gaus",Nrndm);
 hgauss->Draw();
 hstPad->Update(); 
}

// draw a Gaussian on top
TF1 *gaussN=new TF1("gaussN","[0]*gauss",xmin,xmax);
gaussN->SetParameter(0, Nfill*Nrndm * (xmax-xmin)/Nbins);
gaussN->Draw("same");

 // cout<< "weiter? "; cin >> i;
 // delete theCanvas;

return 0;
}