Создание калькулятора в VBA

Dim Firstnum As Double
Dim Secondnum As Double
Dim Answer As Double
Dim Operation As String
 
Private Sub CommandButton0_Click()
    If Screen.Text = "0" Then
        Screen.Text = "0"
    Else
        Screen.Text = Screen.Text + "0"
    End If
    
End Sub
 
Private Sub CommandButton1_Click()
    If Screen.Text = "0" Then
        Screen.Text = "1"
    Else
        Screen.Text = Screen.Text + "1"
    End If
    
End Sub
 
Private Sub CommandButton16_Click()
 
End Sub
 
Private Sub CommandButton2_Click()
    If Screen.Text = "0" Then
        Screen.Text = "2"
    Else
        Screen.Text = Screen.Text + "2"
    End If
    
End Sub
 
Private Sub CommandButton3_Click()
    If Screen.Text = "0" Then
        Screen.Text = "3"
    Else
        Screen.Text = Screen.Text + "3"
    End If
    
End Sub
 
Private Sub CommandButton4_Click()
    If Screen.Text = "0" Then
        Screen.Text = "4"
    Else
        Screen.Text = Screen.Text + "4"
    End If
    
End Sub
 
Private Sub CommandButton5_Click()
    If Screen.Text = "0" Then
        Screen.Text = "5"
    Else
        Screen.Text = Screen.Text + "5"
    End If
    
End Sub
 
Private Sub CommandButton6_Click()
    If Screen.Text = "0" Then
        Screen.Text = "6"
    Else
        Screen.Text = Screen.Text + "6"
    End If
    
End Sub
 
Private Sub CommandButton7_Click()
    If Screen.Text = "0" Then
        Screen.Text = "7"
    Else
        Screen.Text = Screen.Text + "7"
    End If
    
End Sub
 
Private Sub CommandButton8_Click()
    If Screen.Text = "0" Then
        Screen.Text = "8"
    Else
        Screen.Text = Screen.Text + "8"
    End If
    
End Sub
 
Private Sub CommandButton9_Click()
    If Screen.Text = "0" Then
        Screen.Text = "9"
    Else
        Screen.Text = Screen.Text + "9"
    End If
    
End Sub
 
Private Sub CommandButton10_Click()
Screen.Text = ""
Firstnum = Clear
Secondnum = Clear
Answer = Clear
Operation = Clear
   
End Sub
 
Private Sub CommandButton11_Click()
    If Operation = "/" Then
        Answer = Firstnum / Secondnum
        Screen.Text = Answer
        Operation = ""
    ElseIf Operation = "+" Then
        Answer = Firstnum + Secondnum
        Screen.Text = Answer
        Operation = ""
    ElseIf Operation = "-" Then
        Answer = Firstnum - Secondnum
        Screen.Text = Answer
        Operation = ""
    ElseIf Operation = "*" Then
        Answer = Firstnum * Secondnum
        Screen.Text = Answer
        Operation = ""
    End If
End If
 
End Sub
 
Private Sub CommandButton12_Click()
    If Not Screen.Text = "" Then
        Firstnum = Screen.Text
    End If
    Screen = ""
    Operation = "+"
    
End Sub
 
Private Sub CommandButton13_Click()
    If Not Screen.Text = "" Then
        Firstnum = Screen.Text
    End If
    Screen = ""
    Operation = "-"
       
End Sub
Private Sub CommandButton14_Click()
    If Not Screen.Text = "" Then
        Firstnum = Screen.Text
    End If
    Screen = ""
    Operation = "-"
        
End Sub
 
Private Sub CommandButton15_Click()
    If Not Screen.Text = "" Then
        Firstnum = Screen.Text
    End If
    Screen = ""
    Operation = "/"
    
End Sub
 
Private Sub UserForm_Click()
 
End Sub