// the implementation file (source code) for the Particle class //
//---------------------------------------------------------------

// for the source file for any class, we must always include the header file for that class
#include "Particle.h" 
#include <math.h> // Need the sqrt() function for the energy calculation 

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

// this is the default constructor
Particle::Particle() 
{
    
  // if we dont give any arguments, the mass and momentum will be zero
  fMass = 0;
  fP = 0;
}

// This is the normal constructor for an object of the class Particle
// we create the object and assign the appropriate values to its members
Particle::Particle(double mass, double p) 
{

  fMass = mass;
  fP = p;
    
}

double Particle::GetMass() 
{
  return fMass;

}

void Particle::SetMass(double new_mass) 
{
  fMass = new_mass;
}


double Particle::GetMomentum()
{
  return fP;

}

void Particle::SetMomentum(double new_momentum)
{
  fP=new_momentum;

}

double Particle::GetEnergy()
{
  // Calculates the energy of the particle from its mass and its momentum
  
  // By doing this inside the class itself, it greatly simplifies your code
    
  // now in any program with the particle class
  // we can just get the energy using: particle.GetEnergy()

  return sqrt(fMass*fMass+fP*fP);
  
}

// Note that there is NO main() function in this file
// This code cannot be executed on its own (but can be used by another program)