// Header (interface) file for a simple Particle class
// containing 'mass' and 'momentum' information

//Without these lines, "Particle" will not be defined by the compiler
#ifndef __Particle___
#define __Particle___

// to declare a class, use the C++ keyword 'class'
class Particle {

  // the 'members' of this Particle class will be the variables for: mass and momentum (and charge)
    

  // we want them to be private, meaning they can only be accessed inside the class itself
 private: 

  double fMass;
  double fP;
  //double fCharge;  //... etc (could easily add other members)

  // note: I have put an 'f' at the start of the variable names
  // since this is generally the convention that ROOT uses to indicate variables
  // which are members of a class.

  // now we want to list the public parts of the class
  // here we will put the functions that we want to be able to use for the class

 public:

  Particle();
  // the above function is very important - it is called the default constructor
  // for the class. All C++ classes must have a default instructor. 
  // this is the function that is called when you try to create an object of the class, 
  // without any arguments

  Particle(double mass, double p);

  // above is the normal constructor. It makes an object of the class with the given values for m and p (and c)

  // methods:
    
  // basic functions to get and set values of mass and momentum
  double GetMass();
  double GetMomentum();
  //double GetCharge();

  void SetMass(double new_mass);
  void SetMomentum(double new_momentum);
 // void SetCharge(double new_charge);

  // function that calculates the particle energy from the mass and momentum
  
  double GetEnergy();

  // the code that then implements all these functions can be found in the Particle.cc file

}; //  note this semicolon after defining the class!


#endif