/* In this ROOT function we generate the sum of a flat
   distribution nEvents times and fir the output witha straight line.

To run do:
root 
.L foldflat.C // or .L foldflat.C+ to compile or .L foldflat.C++ to force compile
foldflat(100000)
*/

// include C++ STL headers 
#include <iostream>

using namespace std;

// ROOT library obejcts
#include <TH1.h> // 1d histogram classes
#include <TRandom.h> // random generators
#include <TStyle.h> // style object

void foldflat(Int_t nEvents) // nEvents is an argument for the function 
{
  cout << "Generating " << nEvents << " events" << endl << endl;

  // create histogram object
  TH1F* hist = new TH1F("hist", "My first histogram", 100, 0, 1);
  // note that you can declare variable where they are needed!!!

  // create random generator object
  TRandom* randGen = new TRandom();

  // make a loop for the number of events
  for(Int_t n = 0; n < nEvents; n++) {

    if((n+1)%100==0)
      cout << "event " << n+1 << endl;

    hist->Fill(randGen->Rndm()); // fill histogram with flat values 
  }

  // Note that n only has local scope within the lopp so if you do
  // cout << n << endl;
  // the program won't compile!

  // set some options for how to display histogram info when you draw
  // Note that gStyle is a global object in ROOT of the clas TStyle
  gStyle->SetOptStat(1111);
  gStyle->SetOptFit(1111);
 
  hist->SetMinimum(0); // lower y range

  hist->Fit("pol0");
}

// Now you have to work:
// in the command line do:
// .ls // to see list of objects in current directory
// from the commandline do:
// hist->Fit("pol0", "L") // L for maximum likelihood
// Think about this

// try to click on the objects in the graphical window and see what options you get!
// change some options in this program and see the effects
// 1) Fill the hist with a Gauss and fit with a Gauss
// 2) Change back to flat distributions but change the argument so you now can fold it nTimes times and fit with Gauss - when does the distribution get Gaussian
// 3) Why does it get Gaussian?