Implementation of struct date

date.cpp

#include <iostream>

using std::ostream, std::cout;

#include "date.h"

namespace ttime
{
    date::date() : day(1), month(jan), year(1970)
    {
        this->month_lens[feb] += this->is_leap();
    }

    date::date(unsigned day, enum month month, unsigned year) : day(day), month(month), year(year)
    {
        this->month_lens[feb] += this->is_leap();
    }

    bool date::is_leap() const
    {
        return this->year % 4 == 0 && this->year % 100 != 0;
    }

    ostream &operator<<(ostream &l, const date &d)
    {
        const char *const months[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov",
                                       "Dec" };
        return l << d.day << '.' << months[d.month] << '.' << d.year << '\n';
    }

    bool operator<(const date &l, const date &r)
    {
        return l.year < r.year || (l.year == r.year && (l.month < r.month || (l.month == r.month && l.day < r.day)));
    }

    bool operator>(const date &l, const date &r)
    {
        return r < l;
    }

    bool operator>=(const date &l, const date &r)
    {
        return !(l < r);
    }

    bool operator<=(const date &l, const date &r)
    {
        return !(l > r);
    }

    bool operator!=(const date &l, const date &r)
    {
        return l > r || r > l;
    }

    bool operator==(const date &l, const date &r)
    {
        return !(l != r);
    }

    date operator+(const date &This, unsigned num)
    {
        unsigned d = This.day, m = This.month, y = This.year;
        d += num;
        if (d > This.month_lens[m])
        {
            d -= This.month_lens[m];
            if (++m > 12)
            {
                m -= 12;
                ++y;
            }
        }
        date res(d, (enum month) m, y);
        return res;
    }

    date operator++(date &This)
    {
        This = This + 1;
        return This;
    }

    unsigned operator-(const date &This, const date &other)
    {
        if (This == other) return 0;
        if (This < other) return other - This;
        date &smaller = (date &) other;
        unsigned i;
        for (i = 0; This > smaller; ++i, ++smaller);
        return i;
    }

    extern "C" void init()
    {
        date first_day(25, feb, 2008), second_day(1, mar, 2008);
        cout << first_day << second_day;
        cout << second_day - first_day;
    }
}

int main()
{
    ttime::init();

    return 0;
}

date.h

#ifndef DATE_H
    #define DATE_H
#endif // DATE_H

#define months_count 12

#include <ostream>
using std::ostream;

namespace ttime
{
    enum month
    {
        jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec
    };

    struct date
    {

        friend ostream &operator<<(ostream &stream, const date &date);

        friend bool operator<(const date &, const date &);

        bool is_leap() const;

        friend unsigned operator-(const date &, const date &);

        friend date operator+(const date &, unsigned);

        date(unsigned, enum month, unsigned);

        date();

    private:
        unsigned day:5, month:4, year:32 - 5 - 4;
        unsigned month_lens[months_count] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    };

}