Why am I getting a Link error when I try to overload an operator?

Question

I'm doing a project exercise, where I'm revising a previous project of a class I created called Polynomial to use a link list (the original used arrays). The link list uses a template so that any type can be passed into it.

One of the problems I ran into with this project exercise is that I am trying to pass an object of type PolyNumber (from a class I made), and the link list bag I made has a function that compares any item (using ==) that is passed to it.

It works fine with regular types, such as int and string, but runs into problems with custom made object types. So I figured out how to overload the == operator in the PolyNumber class. By itself, it works when I test this class, but when I use this type with the Polynomial class with the Link List implementation, I get errors such as the following for each method in the Polynomial class:

Error   LNK2005 "public: __thiscall PolyNumber::PolyNumber(int,int)" (??0PolyNumber@@QAE@HH@Z) already defined in Polynomial.obj    Project11

Here's my code for those files, but as you can see in the code, there are other files that go with this code, such as the LinkedBag for the link list object, but for space I just include these:

PolyNumber.h

#pragma once

class PolyNumber
{
public:
    PolyNumber();
    PolyNumber(int set_coefficent, int set_degree);
    void setDegree(int set);
    void setCoefficient(int set);
    int getDegree();
    int getCoefficient();
    friend bool operator== (const PolyNumber& p1, const PolyNumber& p2);
    friend bool operator!= (const PolyNumber& p1, const PolyNumber& p2);

private:
    int degree;
    int coefficient;
};

PolyNumber.cpp

#include "PolyNumber.h"


PolyNumber::PolyNumber()
{
    coefficient = 0;
    degree = 0;
}
PolyNumber::PolyNumber(int set_coefficent, int set_degree)
{
    coefficient = set_coefficent;
    degree = set_degree;
}

void PolyNumber::setDegree(int set)
{
    degree = set;
}
void PolyNumber::setCoefficient(int set)
{
    coefficient = set;
}
inline int PolyNumber::getDegree()
{
    return degree;
}
inline int PolyNumber::getCoefficient()
{
    return coefficient;
}

bool  operator== (const PolyNumber& p1, const PolyNumber& p2)
{
    return (p1.coefficient == p2.coefficient && p1.degree == p2.degree);
}

bool operator!= (const PolyNumber& p1, const PolyNumber& p2)
{
    return !(p1 == p2);
}

Polynomial.h

#pragma once
#include "PolynomialInterface.h"
#include "LinkedBag.cpp"
#include "PolyNumber.cpp"
static const int POLYNOMIAL_SIZE = 10;

class Polynomial : public Polynomoal_Interface
{
public:
    //Cunstructs am empty Polynomial  
    Polynomial();

    //Copy constructor
    Polynomial(Polynomial& copy);

    /** Cunstructs a Polynomial with a client defined Polynomial
    @param an array of non-negative integer coeffient that does not exceed POLYNOMIAL_SIZE, each coeffient in the array has a power that correspounds
    to the respective value of the location of the ceffient in that array. */
    Polynomial(int coeffient[POLYNOMIAL_SIZE], int size);

    int degree();
    int coefficient(int power);
    bool changeCoefficient(int newCoefficient, int power);
private:
    //static const int POLYNOMIAL_SIZE = 10;
    //int polynomial[POLYNOMIAL_SIZE];
    LinkedBag<PolyNumber> bag;
};

Polynomial.cpp

#include "Polynomial.h"


Polynomial::Polynomial()
{

}
Polynomial::Polynomial(Polynomial& copy)
{
    std::vector<PolyNumber> copyFrom = copy.bag.toVector();
    for (int i = 0; i < copyFrom.size(); i++)
    {
        bag.add(copyFrom[i]);
    }
}
Polynomial::Polynomial(int coeffient[POLYNOMIAL_SIZE], int size)
{
    for (int i = 0; i <= size; i++)
    {
        PolyNumber number = { coeffient[i], i + 1 };
        bag.add(number);
    }
}
int Polynomial::degree()
{
    int max = 0;
    std::vector<PolyNumber> result = bag.toVector();
    for (int i = 0; i < result.size(); i++)
    {
        if (result[i].getDegree() > max)
        {
            max = result[i].getDegree();
        }
    }
    return max;
}
int Polynomial::coefficient(int power)
{
    int result = 0;
    std::vector<PolyNumber> powerOf = bag.toVector();
    for (int i = 0; i < powerOf.size(); i++)
    {
        if (powerOf[i].getDegree() == power)
        {
            result = powerOf[i].getCoefficient();
        }
    }
    return result;
}
bool Polynomial::changeCoefficient(int newCoefficient, int power)
{
    PolyNumber number = { newCoefficient, power };
    int result = coefficient(power) + newCoefficient;
    bag.remove(number);
    number.setCoefficient(result);
    bag.add(number);
    return true;
}

Answer 1

You have #include "PolyNumber.cpp" instead of #include "PolyNumber.h".

That makes all the methods defined in PolyNumber.cpp to be included (and re-defined) in Polynomial.cpp. The same will happen with LinkedBag.

Why are you including cpps?