【简答题】

 
Private Sub Command1_Click()
    Dim n As Integer, k As Integer, m As Integer
    Dim c As String, a As String
    For k = 0 To 2
        If Op1(k).Value Then
'            n = Val(Op1(k). ? )
        End If
    Next k
    m = Len(Text1.Text)
    a = ""
'    For k = 1 To ?
'        c = Mid$(Text1.Text, ? , 1)
        c = String(1, Asc(c) + n)
        If c > "z" Or c > "Z" And c < "a" Then
            c = String(1, Asc(c) - 26)
        End If
'        ? = a + c
    Next k
    Text2.Text = a
End Sub