A problem about constructor of a class (beginner's question)

I've been writing a library for my program. However, when I tried compiled the program, the debugger told me that I've return a value for the constructor. (Bold part in main code) However, the member function I've included in the constructor should be a void function and it doesn't returned any value at all. Do anybody know what's wrong?

header file:

#include <string>

using std::string;


class Invoice

{

private:

    string PartNumber;

    string PartDescription;

    int Quantity;

    int PricePerItem;

    int InvoiceAmount;

public:

    Invoice(string, string, int, int);

    void setInitial(string, string, int, int);

    void setPartNum(string);

    void setPartDescription (string);

    void setQuantity(int);

    void setPricePerItem(int);

    string getPartNumber();

    string getPartDescription();

    int getQuantity();

    int getPricePerItem();

    int getInvoiceAmount();

}

Main code for the library

#include <iostream>    

using std::cout;

using std::endl;


#include <string>

using std::string;


#include "Invoice.h"


[B]Invoice::Invoice(string part, string description, int number, int money)

{

    setInitial(part, description, number, money);

}[/B]

void Invoice::setInitial(string part, string description, int number, int money)

{

    PartNumber = part;

    PartDescription = description;

    Quantity = number;

    PricePerItem = money;

}

void Invoice::setPartNum(string part)

{

    PartNumber = part;

}

void Invoice::setPartDescription(string description)

{

    PartDescription = description;

}

void Invoice::setQuantity(int number)

{

    if (number >= 0)

        Quantity = number;

    if (number < 0)

    {

        cout << "quanity cannot be negative.\n";

        cout << "quanity set to 0\n";

        Quantity = 0;

    }

}

void Invoice::setPricePerItem(int money)

{

    if (money >= 0)

        PricePerItem = money;

    if (money < 0)

    {

        cout << "pricePerItem cannot be negative.\n";

        cout << "pricePerItem set to 0\n";

        PricePerItem =0;

    }

}

string Invoice::getPartNumber()

{

    return PartNumber;

}

string Invoice::getPartDescription()

{

    return PartDescription;

}

int Invoice::getQuantity()

{

    return Quantity;

}

int Invoice::getPricePerItem()

{

    return PricePerItem;

}

int Invoice::getInvoiceAmount()

{

    if ((Quantity * PricePerItem) >= 0 )

    {

        InvoiceAmount = Quantity * PricePerItem;

        return InvoiceAmount;

    }

    if (Quantity < 0 )

    {

        return 0;

    }

    if (PricePerItem < 0)

    {

        return 0;

    }

}