compilation error message

Hi, any help will be much appreciated.

I'm compiling with the command:
g++ -Wall -o LQueue.C Simulation.C

The message I get is:
Undefined first referenced symbol in file main

Simulation.h

Code:

---

#include <iostream>
#include <ctime>

#ifndef SIMULATION
#define SIMULATION

#include "LQueue.h"

class Simulation
{
  public:
    /***** Function Members *****/
          /***** Constructor *****/
          Simulation();
          /*-----------------------------------------------------------
            Construct a Simulation object.

                Precondition: None.
                Postcondition: Input data members have been initialized
                        with values entered by the user; output data members have
                        been initialized to 0; and random number generator has
                        been initialized.
          -----------------------------------------------------------*/

          /***** Running the simulation *****/
          void run();
          /*-----------------------------------------------------------
            Run the simulation.

                Precondition: None.
                Postcondition: Simulation of airport runway management
                        has been completed and performance statistics is
                        outputted.
          -----------------------------------------------------------*/

          /***** Output *****/
          void display(ostream & out);
          /*-----------------------------------------------------------
            Display results of the simulation.

                Precondition: ostream out is open.
                Postcondition: Simulation process is printed.

      -----------------------------------------------------------*/

          /***** Plane processing *****/
          void managePlanes();
          /*-----------------------------------------------------------
            Manage planes (if any) at the front of landing or takeoff
                queues. 

                Precondition: freeRunway is true.
                Postcondition: Planes are dequeued and put on runway.
          -----------------------------------------------------------*/

          void checkForNewPlane();
          /*---------------------------------------------------------------
            Check if a new plane has arrived and if so, add it to the
                takeoff queue or landing queue depending on different
                circumstances. ((STAR - on h/o))

                Precondition: none.
                Postcondition: takeoff queue or landing queue has been updated.
          ----------------------------------------------------------------*/
 
  private:
          /***** Data Members *****/
            //-- Inputs
            double takeoffRate; //in terms of hrs
                double landingRate; //in terms of hrs
                int landTimeDuration; //in terms of mins
                int takeoffTimeDuration; //in terms of mins
                int lengthOfSimulation; //in mins

                //-- Stats
                int maxPlanesInLandingQ;
                int avgTimeSpentWaitingToLand; //mins
                int maxPlanesInTakeoffQ;
                int avgTimeSpentWaitingToTakeoff; //mins


                int landingTime;
                int takeoffTime;
                bool freeRunway; //some plane is in the process of landing (or not) (if plane takesoff, it's "done") (TRIANGLED)
                int totalMinsWaitingToLand;
                int totalMinsWaitingToTakeoff;

                Queue takeoffQ;
                Queue landingQ;
};

#endif

---

Simulation.C

Code:

---

#include <iostream> // istream, ostream, >>, <<
#include <cstdlib> // rand(), srand()
#include <ctime> //time()
using namespace std;

#include "Simulation.h"

Simulation::Simulation()
{
        //-- Initialize output stats
        maxPlanesInLandingQ = 0;
        avgTimeSpentWaitingToLand = 0; //mins
        maxPlanesInTakeoffQ = 0;
        avgTimeSpentWaitingToTakeoff = 0; //mins

        freeRunway = false;
        totalMinsWaitingToLand = 0;
        totalMinsWaitingToTakeoff = 0;

        //-- get input
        cout << "Enter:/n"
                << "Time for a plane to land (in minutes): ";
                cin >> landingTime;
               
}

void Simulation::run()
{
}

void Simulation::display(ostream & out)
{
}


void Simulation::managePlanes()
{
}

void Simulation::checkForNewPlane()
{
}

---

For sure, there's nothing wrong with LQueue.C and LQueue.h because I've tested those separately.

LOL It turns out I got the error because I didn't have a driver program. :p