Calculate date difference in years, months and days using VB.NET and C#

Recently I needed function that will return the date difference in years, months and days. I didn't find many posts on internet for accured messuring the difference including the leap years, so this is the class I wrote and I hope you will find it useful.

VB code:

Public Class DateSpan
    Public Sub New(ByVal startDate As DateTime, ByVal enddate As DateTime)
        _years = 0
        _months = 0
        _days = 0
        Dim ds As DateSpan = DateDiff(startDate, enddate)
        If Not ds Is Nothing Then
            _years = ds.Years
            _months = ds.Months
            _days = ds.Days
        End If
    End Sub
    Public Sub New()
        _years = 0
        _months = 0
        _days = 0
    End Sub

    Private _years As Integer
    Private _months As Integer
    Private _days As Integer

    Public Property Years() As Integer
        Get
            Return _years
        End Get
        Set(ByVal value As Integer)
            _years = value
        End Set
    End Property
    Public Property Months() As Integer
        Get
            Return _months
        End Get
        Set(ByVal value As Integer)
            _months = value
        End Set
    End Property
    Public Property Days() As Integer
        Get
            Return _days
        End Get
        Set(ByVal value As Integer)
            _days = value
        End Set
    End Property

    Overrides Function ToString() As String
        Return String.Format("{0} year(s)  {1} month(s)  {2} day(s)", _years, _months, _days)
    End Function
    Public Sub Reverse(ByVal reverse As Boolean)
        If reverse Then
            _years = -1 * _years
            _months = -1 * _months
            _days = -1 * _days
        End If
    End Sub

    Public Shared Function DateDiff(ByVal startDate As DateTime, ByVal endDate As DateTime) As DateSpan
        If (startDate = DateTime.MinValue) OrElse (endDate = DateTime.MinValue) Then Return Nothing
        Dim reverse As Boolean = False
        '   reverse the dates
        If startDate > endDate Then
            Dim tmpDate As DateTime = endDate
            endDate = startDate
            startDate = tmpDate
            reverse = True
        End If

        Dim ds As New DateSpan
        '
        '   calculate years
        If startDate.Year = endDate.Year Then
            ds.Years = 0
        Else
            ds.Years = endDate.Year - startDate.Year
        End If
        '
        '   calculate months
        If startDate.Month = endDate.Month Then
            ds.Months = 0
        ElseIf startDate.Month < months =" endDate.Month" months =" 12" day =" endDate.Day" days =" 0" days =" endDate.Day" days =" Date.DaysInMonth(startDate.Year,">= Date.DaysInMonth(endDate.Year, endDate.Month) AndAlso _
                startDate.Day > Date.DaysInMonth(endDate.Year, endDate.Month) Then

                ds.Days = ds.Days - Date.DaysInMonth(endDate.Year, endDate.Month)
            Else
                If ds.Months = 0 Then
                    ds.Years -= 1
                    ds.Months = 11
                Else
                    ds.Months -= 1
                End If
            End If
        End If
        '
        '   reverse date (show negative difference)
        ds.Reverse(reverse)
        Return ds
    End Function



End Class

C# code:

    public class DateSpan
    {

        private int _years = 0;
        private int _months = 0;
        private int _days = 0;

        public int Years
        {
            get { return _years; }
            set { _years = value; }
        }
        public int Months
        {
            get { return _months; }
            set { _months = value; }
        }
        public int Days
        {
            get { return _days; }
            set { _days = value; }
        }

        public override string ToString()
        {
            return string.Format("{0:00}year(s) {1:00} month(s) {2:00} day(s)", _years, _months, _days);
        }
        public void Reverse(bool reverse)
        {
            if (reverse)
            {
                _years = -1 * _years;
                _months = -1 * _months;
                _days = -1 * _days;
            }
        }

        public static DateSpan DateDiff(DateTime startDate, DateTime endDate)
        {
            if ((startDate == null)  (endDate == null)) return null;
            bool reverse = false;
            // reverse the dates
            if (startDate > endDate)
            {
                DateTime tmpDate = endDate;
                endDate = startDate;
                startDate = tmpDate;
                reverse = true;
            }

            DateSpan ds = new DateSpan();
            //
            // calculate years
            if (startDate.Year == endDate.Year)
            {
                ds.Years = 0;
            }
            else
            {
                ds.Years = endDate.Year - startDate.Year;
            }
            //
            // calculate months
            if (startDate.Month == endDate.Month)
            {
                ds.Months = 0;
            }
            else if (startDate.Month < months =" endDate.Month" months =" 12" day ="=" days =" 0;" days =" endDate.Day" days =" System.DateTime.DaysInMonth(startDate.Year,">= System.DateTime.DaysInMonth(endDate.Year, endDate.Month) && startDate.Day > System.DateTime.DaysInMonth(endDate.Year, endDate.Month))
                {

                    ds.Days = ds.Days - System.DateTime.DaysInMonth(endDate.Year, endDate.Month);
                }
                else
                {
                    if (ds.Months > 0)
                    {
                        ds.Months -= 1;
                    } else {
                        ds.Months = 11;
                        ds.Years -= 1;
                    }
                }
            }
            //
            // reverse date (show negative difference)
            ds.Reverse(reverse);
            return ds;
        }
    }