Aggregation using C++ - c++

Question

I am trying to make one class work with another class. It is supposed to decrement the member of the other class.
my first class is
class Bike
{
private:
int miles;
Speedometer speedom;
static int fuelCount;
public:
Bike();
Bike(int, Speedometer*); //Problem occurs here
~Bike();
int getMiles();
int getFuelCount();
void incrementMiles();
};
int Bike::fuelCount = 0;
Bike::Bike()
{
miles = 0;
fuelCount++;
}
Bike::Bike(int m, Speedometer * spm) //This is where I am having problems
{
miles = m;
speedom = &spm;
}
Bike::~Bike()
{
cout << "The Bike's destructor is running." << endl;
fuelCount--;
}
int Bike::getMiles()
{
return miles;
}
int Bike::getFuelCount()
{
return fuelCount;
}
void Bike::incrementMiles()
{
miles++;
if (miles == 999999)
miles = 0;
}
The other class which is supposed to be included in the first is:
Class Speedometer
{
private:
int fuel;
public:
Speedometer();
Speedometer(int);
~Speedometer();
int getFuel();
void incrementFuel();
void decrementFuel();
};
Speedometer::Speedometer()
{
fuel = 0;
}
Speedometer::Speedometer(int f)
{
fuel = f;
}
int Speedometer::getFuel()
{
return fuel;
}
void Speedometer::incrementFuel()
{
if (fuel <= 15)
fuel++;
}
void Speedometer::decrementFuel()
{
if (fuel > 0)
fuel--;
}
They are supposed to work together. Bike is to be able to work with speedometer object. It should decrease the speedometers current amount of fuel by one gallon for every 24 miles traveled.
This is supposed to be a aggregate relationship not composition.
Please help me just understand how to make that relationship and how its supposed to be called.
Thank you in advance.
here is my main function
btw - i have all the right #includes i just have not listed them here
int main(int argc, char *argv[])
{
Speedometer a(999970, spd);
for(int count = 0; count <=24; count++)
a.decrementMiles();
while (a.getFuel() > 0)
{
a.incrementMiles();
cout<< "Miles:" << a.getMiles() << endl;
cout<< "Fuel:" << a.getFuel() << endl;
}
return 0;
}

Answer 1

You have a large number of issues here.
First of all, in your main(), you construct your Speedometer object with a constructor you have not implemented. The only constructors you have defined are the default constructor and Speedometer(int). You then call Speedometer(int, ???), the ??? being spd because you do not declare spd anywhere in the code you have provided, so we have no idea what it is.
It's really impossible to say what's wrong with your code in its current state.

Answer 2

As written, you've made a composition; Speedometer is part of Bike since it is a field. To make it an aggregation, make Bike hold a pointer to Speedometer. Note that as a consequence, you'll probably need Bike to create or obtain an initial Speedometer (could be NULL to begin with, or pass one in the constructor), and you might want to add accessor methods to Bike in order to add/remove/change the Speedometer.
[edit] Bike might also need to know how to dispose of the Speedometer properly in order to avoid leaking it.
[edit 2] Also as #cjm571 pointed out, your main function is creating and operating directly upon a "disembodied" Speedometer. Shouldn't it be on a Bike? :)

Answer 3

#include <iostream>
using namespace std;
class Bike
{
private:
int miles;
static int fuelCount;
// Speedometer speedom;
public:
Bike();
Bike(int); // Speedometer *); check comment on line 82
~Bike();
int getMiles();
int getFuelCount();
void incrementMiles();
};
int Bike::fuelCount = 0;
Bike::Bike()
{
miles = 0;
fuelCount++;
}
Bike::Bike(int m)//Speedometer (*spm) I don't see the purpose of this in the current state of the program, I may not be seing the whole picture
{
miles = m;
/* speedom = spm; remember, there must be a parent and a child class, at the current state you'r trying
to call a child from parent, the child class has not been defined, so i switched them and now Bike is a chiled. */
}
Bike::~Bike()
{
cout << "The Bike's destructor is running." << endl;
fuelCount--;
}
int Bike::getMiles()
{
return miles;
}
int Bike::getFuelCount()
{
return fuelCount;
}
void Bike::incrementMiles()
{
miles++;
if (miles == 999)
miles = 0;
}
class Speedometer
{
private:
int fuel;
public:
Speedometer();
Speedometer(int f);
int getFuel();
Bike theBike; // This is what you needed in order to make incrementMiles to work.
void incrementFuel();
void decrementFuel();
};
Speedometer::Speedometer()
{
fuel = 0;
}
Speedometer::Speedometer(int f)
{
fuel = f;
}
int Speedometer::getFuel()
{
return fuel;
}
void Speedometer::incrementFuel()
{
if (fuel <= 15)
fuel++;
}
void Speedometer::decrementFuel()
{
if (fuel > 0)
fuel--;
}
int main(int argc, char *argv[])
{
Speedometer a(999); //You never declared this, did you mean spm???
for(int count = 0; count <=24; count++)
a.theBike.incrementMiles();
while (a.getFuel() > 0)
{
a.theBike.incrementMiles();
cout<< "Miles:" << a.theBike.getMiles() << endl;
cout<< "Fuel:" << a.getFuel() << endl;
}
cin.get();
return 0;
} //There is no break declared (that i can see at least) so the program runs an infinite loop
// Don't want to add too many things to it, I don't know what your plan is.
// Hoping to have made it clearer.