Перегрузка операций и функций

#include <iostream>
 
using namespace std;
 
 
 
class Date
{
    int day;
    int month;
    int year;
 
    static unsigned long From_Date_To_Days(Date d);
    static Date From_Days_To_Date(unsigned long n);
 
    friend Date operator+(Date d, int n);
    friend Date operator-(Date d, int n);
    friend int operator%(Date d1, Date d2);
    friend ostream& operator<<(ostream& os, Date d);
 
public:
    Date(int d, int m, int y);
 
};
 
/////////////////OPERATORS////////////////////////////////
 
Date operator+(Date d, int n);
Date operator-(Date d, int n);
int operator%(Date d1, Date d2);
ostream& operator<<(ostream& os, Date d);
///////////////////////////////////////////////////////////
 
 
 
int main()
{
    Date d1(9, 12, 2013);
    Date d2(29, 11, 2013);
    Date d3 = d1 + 10;
    Date d4 = d2 - 365*2;
    int i1 = d2%d1;
    cout << d1 << endl << d2 << endl << d3 << endl << d4 << endl << i1 << endl;
    system("pause");
}
 
 
////////////////////////////////////////////////
//////////////////DEFINITION////////////////////
////////////////////////////////////////////////
 
 
Date::Date(int d, int m, int y)
{
    this->day = d;
    this->month = m;
    this->year = y;
}
 
 
Date operator+(Date d, int n)
{
    return Date::From_Days_To_Date(Date::From_Date_To_Days(d) + n);
}
 
 
Date operator-(Date d, int n)
{
    return d+(-n);
}
 
 
int operator%(Date d1, Date d2)
{
    return Date::From_Date_To_Days(d2) - Date::From_Date_To_Days(d1);
}
 
 
ostream& operator<<(ostream& os, Date d)
{
    os << d.day << '.' << d.month << '.' << d.year;
    return os;
}
 
 
unsigned long Date::From_Date_To_Days(Date d)
{
    unsigned long a = (14 - d.month) / 12;
    unsigned long y = d.year + 4800 - a;
    unsigned long m = d.month + 12 * a - 3;
    return (d.day + (153 * m + 2) / 5 + 365 * y + y / 4 - y / 100 + y / 400 - 32045);
}
 
 
Date Date::From_Days_To_Date(unsigned long jdn)
{
    unsigned long a = jdn + 32044;
    unsigned long b=(4*a+3)/146097;
    unsigned long c = a - (146097 * b) / 4;
    unsigned long d = (4 * c + 3) / 1461;
    unsigned long e = c - (1461 * d) / 4;
    unsigned long m = (5 * e + 2) / 153;
    int day = e - (153 * m + 2) / 5 + 1;
    int month = m + 3 - 12 * (m / 10);
    int year = 100 * b + d - 4800 + (m / 10);
    return Date(day, month, year);
}