' AddMonth Excel Function
' Copyright 1393, Jalil Aryan Yegane
' http://www.papyrus.ir/Pages/3364
Function AddMonth(sDate As String, iMonth) As String
    Dim WrdArray() As String
    Dim y, m, d As Integer
    Dim sm, sd As String
    WrdArray() = Split(sDate, "/")
    y = 0
    m = 0
    d = 0
    If UBound(WrdArray()) + 1 = 3 Then
        y = Cint(WrdArray(0))
        m = Cint(WrdArray(1))
        d = Cint(WrdArray(2))
        If y < 100 Then
            y = 1300 + y
        End If
        If IsValidShDate(y, m, d) Then
            isLeapYear = Jleap(y)
            For i = 1 To iMonth
                m = m + 1
                If m > 12 Then
                    m = 1
                    y = y + 1
                End If
            Next
            If d = 31 And (m > 6 And m <= 12) Then
                d = 30
            End If
            If d = 30 And m = 12 And isLeapYear = False Then
                d = 29
            End If
            If d = 30 And m = 12 And isLeapYear Then
                d = 30
            End If
            If m < 10 Then
                sm = "0" & m
            Else
                sm = m
            End If
            If d < 10 Then
                sd = "0" & d
            Else
                sd = d
            End If
            AddMonth = y & "/" & sm & "/" & sd
        Else
            AddMonth = "تاریخ ورودی نامعتبر"
        End If
    Else
        AddMonth = "فرمت تاریخ ورودی نامعتبر"
    End If
End Function

Function IsValidShDate(ByVal y As Integer, ByVal m As Integer, ByVal d As Integer) As Boolean
    If (y >= 1 And m >= 1 And m <= 12 And d >= 1 And d <= ShMonthDayCount(y, m)) Then
        IsValidShDate = True
    Else
        IsValidShDate = False
    End If
End Function

Function Jleap(ByVal Year As Integer) As Boolean
    Dim tmp As Integer
    tmp = Year Mod 33
    If (tmp = 1 Or tmp = 5 Or tmp = 9 Or tmp = 13 Or tmp = 17 Or tmp = 22 Or tmp = 26 Or tmp = 30) Then
        Jleap = True
    Else
        Jleap = False
    End If
End Function

Function ShMonthDayCount(ByVal y As Integer, ByVal m As Integer) As Integer
    Dim result As Integer
        If m <= 6 Then
            result = 31
        Else
            If m <= 11 Then
                result = 30
            Else
                If Jleap(y) Then
                    result = 30
                Else
                    result = 29
                End If
            End If
        End If
    ShMonthDayCount = result
End Function