Not getting decreasing gas in a C++ program - class

Question

Ok, so I have this program that is suppose to simulate an "Uber" driver picking up and dropping off customers and informing him of how far he has driven and how much gas he should have felt. I basically have it all worked out but for the life of me I can't get the gas to go down it stays at a static number. I know it is probably something so simple its dumb but I can't see it.
in my FuelGauge.h
#ifndef FuelGauge_h
#define FuelGauge_h
#define MAXG 15
// Class FuelGauge definition
class FuelGauge
{
// Data member
static int gallons;
public:
// Overloading -- operator
void operator --()
{
--gallons;
}// End of function
// Function to return gallons
int getGallons()
{
return gallons;
}// End of function
};// End of class
// Initializes static data member
int FuelGauge::gallons = MAXG;
#endif /* FuelGauge_hpp */
in my Car.h
#ifndef Car_h
#define Car_h
#include "FuelGauge.h"
#include "Odometer.h"
// Class car definition
class Car
{
public:
// Declares object as data member using deligation
FuelGauge *fg;
Odometer *om;
// Overloads >> operator
friend std::istream & operator >>(std::istream &is, Car &c)
{
int no;
// Loops till valid mileage entered by the user
do
{
// Accepts mileage
std::cin>>no;
// Checks if the mileage is zero or negative show error message
if(no <= 0)
std::cout<<"\n Invalid response, mileage should be greater than 0. \n Please reenter data.";
// Otherwise come out of the loop
else
break;
}while(1);
// Loops till no
for(int x = 0; x < no; x++)
// Increase the mileage by one
++*c.om;
// Checks if the current mileage is greater than or equals to 24 and entered mileage is less than 24
if(c.om->getCurrentMileage() >= 24 && no < 24)
// Decrement by one
--*c.fg;
// Otherwise
else
{
// Calculate the remainder
int rem = (no / 24);
// Loops till remainder
for(int x = 0; x < rem; x++)
// Decrease by one
--*c.fg;
}// End of else
// return istream object
return is;
}// End of function
// Overload << operator
friend std::ostream & operator <<(std::ostream &os, Car &c)
{
// Checks if the current gallon is less than or equals to zero
if(c.fg->getGallons() <= 0)
{
// Display message and stop
std::cout<<"\n Drove "<<c.om->getCurrentMileage()<<" miles I'm out of gas.";
exit(0);
}// End of if condition
// Otherwise display total mileage traveled and fuel left
else
std::cout<<"\n Drove "<<c.om->getCurrentMileage()<<" miles now I have "<<c.fg->getGallons()<<" gallons left.";
return os;
}// End of function
};// End of class
#endif /* Car_hpp */
and lastly Main.cpp
#include<iostream>
#include<stdlib.h>
#include "FuelGauge.h"
#include "Odometer.h"
#include "Car.h"
using namespace std;
// main function definition
int main()
{
int customer = 1;
// Creates car object
Car cc;
// Loops till = 0 fuel available
do
{
// Accepts data and displays data using object
cout<<"\n How far away is customer #"<<customer<<"? ";
cin>>cc;
cout<<cc;
cout<<"\n How far does customer #"<<customer<<" need to go?";
cin>>cc;
cout<<cc;
}while(static_cast<void>(customer++),1);// End of do - while
}// End of main function
I believe that problem is in my FuelGauge.h but I'm not seeing it. If someone would be so kind to look it over and let me know if they see anything I would greatly appreciate it.