Why are my calculations off?

Question

I'm practically done with this program. My only issue is my calculations, I guess. My numbers are completely off. I am too new to post an image, so here is the link to my output. Example: http://imageshack.us/photo/my-images/62/16902078.jpg/

NumDays.h

#ifndef NUMDAYS_H
#define NUMDAYS_H
#include <iostream>
#include <math.h>
using namespace std;

class NumDays
{
private:
    double hours, days;
    void calcDays();
public:
    // Constructors
    NumDays();
    NumDays(double);
    // Mutator Functions
    void setHours(double);

    // Accessor Functions
    double getHours();
    double getDays();

    // Overloaded operator functions
    NumDays operator + (const NumDays &);   // Overloaded +
    NumDays operator - (const NumDays &);   // Overloaded -
    NumDays operator ++ ();                 // Overloaded Prefix ++
    NumDays operator ++ (int);              // Overloaded Postfix ++
    NumDays operator -- ();                 // Overloaded Prefix --
    NumDays operator -- (int);              // Overloaded Postfix --

};
#endif

NumDays.cpp

// Implementation file for the NumDays class
#include <iostream>
#include <math.h>
#include "NumDays.h"
using namespace std;

// Recalculation function
void NumDays::calcDays()
{
    days = hours / 8;
}

// Default Constructor
NumDays::NumDays()
{
    hours = 0;
    days = 0;
}

// Constructor 1
NumDays::NumDays(double h)
{
    hours = h;         
    days = hours * 1 / 8;   
}


// Mutatory Functions
void NumDays::setHours(double h)
{
    hours = h;
}


// Accessor Functions
double NumDays::getHours()
{
    return hours;
}

double NumDays::getDays()
{
    NumDays::calcDays();
    return days;
}


// Overloaded operator functions
NumDays NumDays::operator + (const NumDays &a)
{
    NumDays temp;
    temp.hours = this->hours + a.hours;
return temp;
}

NumDays NumDays::operator - (const NumDays &a)
{
    NumDays temp;
    temp.hours = this->hours + a.hours;
    return temp;
}


NumDays NumDays::operator ++ ()
{
    ++hours;
    calcDays();
    return *this;
}

NumDays NumDays::operator -- ()
{
    --hours;
    calcDays();
    return *this;
}

NumDays NumDays::operator ++ (int)
{
    NumDays temp(*this);
    ++hours;
    return temp;
}

NumDays NumDays::operator -- (int)
{
    hours--;
    calcDays();
    return *this;
}

main.cpp

#include <iostream>
#include "NumDays.h"
using namespace std;

int main()
{
    double hours1, hours2;

    //Prompt for the data for the first 2 objects
    cout << "Enter the number of hours for the the object called One: ";
    cin >> hours1;
    cout << "Enter the number of hours for the the object called Two: ";
    cin >> hours2;

    // Define two objects of WorkHours
    NumDays one(hours1), two(hours2);

    cout << "One: " << one.getDays() << " day(s)" << endl;
    cout << "Two: " << two.getDays() << " day(s)" << endl << endl;

    // Demonstrate addition and subtraction operators
    cout << "Three = One + Two: " << (one - two).getDays() << " day(s)" << endl;
    cout << "One - Two: " << (one - two).getDays() << " day(s)" << endl << endl;

    // Define a third and fourth object to be used for further operator demonstrations
    NumDays three(one + two), four;

    // Demonstrate increment and decrement operators
    four = three++;
    cout << "Four = Three++ " << endl;
    cout << " Three: " << three.getDays() << " day(s)" << endl;
    cout << " Four: " << four.getDays() << " day(s)" << endl << endl;

    four = ++three;
    cout << "Four = ++Three: " << endl;
    cout << " Three: " << three.getDays() << " day(s)" << endl;
    cout << " Four: " << four.getDays() << " day(s)" << endl << endl;

    four = three--;
    cout << "Four = Three--: " << endl;
    cout << " Three: " << three.getDays() << " day(s)" << endl;
    cout << " Four: " << four.getDays() << " day(s)" << endl << endl;

    four = --three;
    cout << "Four = --Three: " << endl;
    cout << " Three: " << three.getDays() << " day(s)" << endl;
    cout << " Four: " << four.getDays() << " day(s)" << endl;

    system("pause");
    return 0;
}

Answer 1

So, where is the implementation of your operator << function?

The code you posted contains none. You declared it as a friend in NumDays.h

friend ostream &operator << (ostream &, NumDays &);

but there's no definition for it either in NumDays.cpp or anywhere else.

Obviously, the linker is telling you that it can't find it. Neither can I.

You have to go to your NumDays.cpp and implement your operators << and >> there

ostream &operator << (ostream &s, NumDays &n)
{
  // Whatever
  return s;
}

istream &operator >> (istream &s, NumDays &n);
{
  // Whatever
  return s;
}