Editing A simple main() method of Geant4

The contents of main() will vary according to the needs of a given simulation application and therefore must be supplied by the user

First you must include all of the files you will be calling into the main() method
 #include "G4RunManager.hh"
 #include "G4UImanager.hh"

 #include "ExG4DetectorConstruction01.hh"
 #include "ExG4PhysicsList00.hh"
 #include "ExG4ActionInitialization01.hh"
Secondly construct the default run manager
  G4RunManager* runManager = new G4RunManager;
Then you need to set the mandatory initialization classes
 runManager->SetUserInitialization(new ExG4DetectorConstruction01);
 runManager->SetUserInitialization(new ExG4PhysicsList00);
 runManager->SetUserInitialization(new ExG4ActionInitialization01);
 //this code initializes G4DetectorConstruction, G4PhysicsList, G4ActionInitialization
Initialization of the G4 kernel
 runManager->Initialize();
The next step for a simple main() method would be getting the pointer to the UI(User Interface) manager and set verbosities
 G4UImanager* UI = G4UImanager::GetUIpointer();
 UI->ApplyCommand("/run/verbose 1");
 UI->ApplyCommand("/event/verbose 1");
 UI->ApplyCommand("/tracking/verbose 1")
Starting the run process
 int numberOfEvent = 3; //you can put however many events you would like this example is set at 3.
 runManager->BeamOn(numberOfEvent);
Then you need to terminate the job and close the main() method
 delete runManager;
   return 0;
 }