关于时间的加减计算

前几天论坛上有人问我时间加减运算的办法，也就是类似5:5+6:6=11:11。
于是有了代码：

        Dim temp_h, temp_m As Double
        Select Case Op
            Case "+"
                T2 = Split(TxtTime.Text, ":")
                If T2.Length = 2 Then
                    temp_m = CDbl(T1(1)) + CDbl(T2(1))
                    temp_h = CDbl(T1(0)) + CDbl(T2(0))
                    If temp_m >= 60 And temp_m < 120 Then
                        temp_h += 1
                        temp_m -= 60
                        TxtTime.Text = CStr(temp_h) + ":" + CStr(temp_m)
                        ListBox1.Items.Add(TxtTime.Text)
                    ElseIf temp_m >= 0 And temp_m < 60 Then
                        TxtTime.Text = CStr(temp_h) + ":" + CStr(temp_m)
                        ListBox1.Items.Add(TxtTime.Text)
                    ElseIf temp_m >= 120 Then
                        MsgBox("分钟数错误")
                    End If
                Else
                    MsgBox("仅允许一个冒号")
                    Op = ""
                    Exit Sub
                End If
            Case "-"
                T2 = Split(TxtTime.Text, ":")
                If T2.Length = 2 Then
                    temp_m = CDbl(T1(1)) - CDbl(T2(1))
                    temp_h = CDbl(T1(0)) - CDbl(T2(0))
                    If temp_m < 0 And temp_m >= -60 Then
                        temp_h -= 1
                        temp_m += 60
                        TxtTime.Text = CStr(temp_h) + ":" + CStr(temp_m)
                        ListBox1.Items.Add(TxtTime.Text)
                    ElseIf temp_m >= 0 And temp_m < 60 Then
                        TxtTime.Text = CStr(temp_h) + ":" + CStr(temp_m)
                        ListBox1.Items.Add(TxtTime.Text)
                    ElseIf temp_m <= -120 Then
                        MsgBox("分钟数错误")
                    End If
                Else
                    MsgBox("仅允许一个冒号")
                    Op = ""
                    Exit Sub
                End If
            Case ""
                    Exit Sub
        End Select

不过有了新问题,类似7:85这样的非标准时间不能算，于是将加减代码换掉。可是新的问题又来了，他们想一次输入数据类似1:1+2:2+3:3= 一次计算。我有想到了原来写的一个表达式解析类。这个实在太复杂，正则表达式应该ok。徘徊中~~~