vb 程序设计 关于一个日历程序的问题

Dim selectedate%

Private Sub cbomonth_click()
Call setday
Call lblnumber_click(selectedate% - 1)
End Sub

Private Sub cboyear_Click()
Static once% ' 改变年度
If Not once Then
    once = True
    Exit Sub
End If
Call cbomonth_click

End Sub

Private Sub checkdate(month1%, year1%)
Dim i%, value%, date1$

For i% = 28 To 32
    date1$ = (Str$(month1%) + "/" + Str$(i%) + "/" + Str$(year1%))
        If IsDate(date1$) Then
            value% = i%
        Else
            Call displaynumbers(value%)
            Exit Sub
        End If
Next i%
End Sub

Private Sub cmdcancel_Click()
Unload frmcalendar
End Sub

Private Sub cmdok_Click()
Dim month1%, day1%, year1%, date1$
day1% = selectedate%
month1% = cbomonth.ListIndex + 1
year1% = cboyear.ListIndex + 1960
date1$ = (Str$(month1%) + "/" + Str$(day1%) + "/" + Str$(year1%))
date1$ = Format$(date1$, "general date")

MsgBox Format$(date1$, "long date") '显示你选择的日期

End Sub

Private Function determinemonth%()
Dim i%
i% = cbomonth.ListIndex '选择的月份
determinemonth% = i% + 1
End Function

Private Function determineyear%()
Dim i%
i% = cboyear.ListIndex '选择的年度
If i% = -1 Then Exit Function
determineyear% = CInt(Trim(cboyear.List(i%)))
End Function

Private Sub displaynumbers(number%)
Dim i%
For i% = 28 To 30
    lblnumber(i%).Visible = False
Next i%
For i% = 28 To number% - 1
    lblnumber(i%).Visible = True
Next i%

End Sub

Private Sub fillcbomonth()
cbomonth.AddItem "一月"
cbomonth.AddItem "二月"
cbomonth.AddItem "三月"
cbomonth.AddItem "四月"
cbomonth.AddItem "五月"
cbomonth.AddItem "六月"
cbomonth.AddItem "七月"
cbomonth.AddItem "八月"
cbomonth.AddItem "九月"
cbomonth.AddItem "十月"
cbomonth.AddItem "十一月"
cbomonth.AddItem "十二月"
End Sub

Private Sub fillcboyear()
Dim i%
For i% = 1960 To 2060 '填充年度
    cboyear.AddItem Str$(i%)
Next i%

End Sub

Private Sub Form_Load()

selectedate% = CInt(Format$(Now, "dd"))

'填充月份下拉框
Call fillcbomonth

'填充年份下拉框
Call fillcboyear

'设置当前时间
Call setdate

'显示当前是星期几
Dim caption1$
Dim r As Integer
r = Weekday(Date)
If r = 1 Then
    caption1$ = "星期天"
ElseIf r = 2 Then
    caption1 = "星期一"
ElseIf r = 3 Then
    caption1 = "星期二"
ElseIf r = 4 Then
    caption1 = "星期三"
ElseIf r = 5 Then
    caption1 = "星期四"
ElseIf r = 6 Then
    caption1 = "星期五"
Else
    caption1 = "星期六"
End If
lblday.Caption = caption1$

End Sub

Private Sub lblnumber_click(Index As Integer)
Dim i%
On Error GoTo err1
For i% = 0 To 30
    lblnumber(i%).BorderStyle = 0
Next i%
If lblnumber(Index).BorderStyle = 1 Then
    lblnumber(Index).BorderStyle = 0
Else
    lblnumber(Index).BorderStyle = 1
End If
selectedate% = Index + 1
Dim month1%, day1%, year1%, date1$
day1% = selectedate%
month1% = cbomonth.ListIndex + 1
year1% = cboyear.ListIndex + 1960
date1$ = (Str$(month1%) + "/" + Str$(day1%) + "/" + Str$(year1%))
Dim r%
Dim caption1$
r% = Weekday(date1$)
If r% = 1 Then
    caption1$ = "星期天"
ElseIf r% = 2 Then
    caption1 = "星期一"
ElseIf r% = 3 Then
    caption1 = "星期二"
ElseIf r% = 4 Then
    caption1 = "星期三"
ElseIf r% = 5 Then
    caption1 = "星期四"
ElseIf r% = 6 Then
    caption1 = "星期五"
Else
    caption1 = "星期六"
End If
lblday.Caption = caption1$
lbldate.Caption = Format$(date1$, "long date")

err1:
    If Err = 0 Then Exit Sub
    If Err = 13 Then
        selectedate% = selectedate% - 1
    Exit Sub
    End If
    End Sub

Private Sub setdate()
'年份
Dim r%, i%
r% = CInt(Format$(Now, "yyyy"))
i% = r% - 1960
cboyear.ListIndex = i%

'月份
r% = CInt(Format$(Now, "mm"))
cbomonth.ListIndex = (r% - 1)

'日期
r% = CInt(Format$(Now, "dd"))
lblnumber(r% - 1).BorderStyle = 1
selectedate% = r%

End Sub

Private Sub setday()
Dim month1%, year1%
month1% = determinemonth()
year1% = determineyear()
Call checkdate(month1%, year1%)
End Sub

谁能详细解释一下这段程序

差不多，太长没心思写