做了一个计算机，但是只可以以鼠标点击数字输入，不可以以键盘输入，应该怎么解决？

0-9建立的是一个按钮数组，代码如下，请指教加入怎么样的代码可以从键盘输入相应的数字？
代码：
Option Explicit
Dim Operand1 As Double, Operand2 As Double
Dim Operator As String
Dim ClearDisplay As Boolean

Private Sub ClearBttn_Click()
Display.Caption = ""
End Sub

Private Sub Digits_Click(Index As Integer)
If ClearDisplay Then
Display.Caption = ""
ClearDisplay = False
End If
Display.Caption = Display.Caption + Digits(Index).Caption
End Sub

Private Sub Div_Click()
Operand1 = Val(Display.Caption)
Operator = "/"
Display.Caption = ""
End Sub

Private Sub DotBttn_Click()
If InStr(Display.Caption, ".") Then
Exit Sub
Else
Display.Caption = Display.Caption + "."
End If
End Sub

Private Sub Equals_Click()
Dim result As Double

On Error GoTo ErrorHandler
Operand2 = Val(Display.Caption)
If Operator = "+" Then result = Operand1 + Operand2
If Operator = "-" Then result = Operand1 - Operand2
If Operator = "*" Then result = Operand1 * Operand2
If Operator = "/" And Operand2 <> "0" Then result = Operand1 / Operand2
Display.Caption = result
ClearDisplay = True
Exit Sub
ErrorHandler:
MsgBox "The operation resulted in the following error" & vbCrLf & Err.Description
Display.Caption = "ERROR"
ClearDisplay = True
End Sub

Private Sub Minus_Click()
Operand1 = Val(Display.Caption)
Operator = "-"
Display.Caption = ""
End Sub

Private Sub Over_Click()
If Val(Display.Caption) <> 0 Then Display.Caption = 1 / Val(Display.Caption)
End Sub

Private Sub Plus_Click()
Operand1 = Val(Display.Caption)
Operator = "+"
Display.Caption = ""
End Sub

Private Sub PlusMinus_Click()
Display.Caption = -Val(Display.Caption)
End Sub

Private Sub Times_Click()
Operand1 = Val(Display.Caption)
Operator = "*"
Display.Caption = ""
End Sub