This example contains four functions that determine whether a year is a leap year. When the program starts, it uses each to see which years between 1880 and 2020 are leap years and adds them to four list boxes, one for each function. If you make the form tall enough, you can see that they all agree.

Public Function IsLeapYear0(ByVal y As Integer) As Boolean
    On Error Resume Next
    IsLeapYear0 = False
    'If the year is evenly divisible by 4 and not by 100,
    ' then this
    'is a leap year.
    If y Mod 4 = 0 And y Mod 100 <> 0 Then
        IsLeapYear0 = True
        'If the year is evenly divisible by 4 and 100, then
        ' check to
        'see if the quotient of year divided by 100 is also
        ' evenly
        'divisible by 4. If it is, then this is a leap year.
    ElseIf y Mod 4 = 0 And y Mod 100 = 0 Then
        If (y \ 100) Mod 4 = 0 Then IsLeapYear0 = True
    End If
End Function

Private Function IsLeapYear1(ByVal y As Integer) As Boolean
    If y Mod 4 <> 0 Then Return False
    If y Mod 400 = 0 Then Return True
    If y Mod 100 = 0 Then Return False
    Return True
End Function

Private Function IsLeapYear2(ByVal y As Integer) As Boolean
    Return (y Mod 4 = 0) AndAlso _
        ((y Mod 100 <> 0) OrElse (y Mod 400 = 0))
End Function

Private Function IsLeapYear3(ByVal y As Integer) As Boolean
    Return IsDate("2/29/" & y)
End Function

    If DateTime.IsLeapYear(i) Then lstDateTime.Items.Add(i)