Erase Previously selected data - vba

Question

I am currently working on a drawing generating code for AutoCAD, in order for the drawing to be generated certain options have to be chosen , and when a wrong option is chosen the person can be able to click on back to go and rectify the option. Here is my code below, the problem is that the code does not erase the previously selected data when "back" is clicked, for example, if I choose "SBPP" the click enter and it takes me to "Louvres" option, then I want to go back and change from "SBPP" to "STD Piping", the previously selected "SBPP" must be erased :
Sub DWG ()
Pump: ans = InputBox("1 = STD Piping" & vbCrLf & _
"2 = Omit Pump" & vbCrLf & _
"3 = SBPP", "Pump Piping")
Select Case ans
Case "1":
: Set layerObj = ThisDrawing.Layers.Add("PUMP_PIPING_" & Size)
layerObj.LayerOn = True
Case "2":
: Set layerObj = ThisDrawing.Layers.Add("OMIT_PUMP_" & Size)
layerObj.LayerOn = True
Case "3":
: Set layerObj = ThisDrawing.Layers.Add("STBP_" & Size)
layerObj.LayerOn = True
Case Else: MsgBox "Wrong Input Dude.", vbCritical, MSG: Exit Sub
End Select
'______________________________________________________________________________
'Option for Louvres
Louver: ans = InputBox("1 = STD Louvers" & vbCrLf & _
"2 = IND louvers" & vbCrLf & _
"3 = Back ", "Pump Piping")
Select Case ans
Case "1":
: Set layerObj = ThisDrawing.Layers.Add("LOUVRES_STD")
layerObj.LayerOn = True
Case "2":
: Set layerObj = ThisDrawing.Layers.Add("LOUVRES_INDUS")
layerObj.LayerOn = True
Case "3":
If ans = 3 Then
GoTo Pump
End If
Case Else: MsgBox "Wrong Input Dude.", vbCritical, MSG: Exit Sub
End Select
End Sub
How can I modify this code so that when "back" is clicked it erases previously selected data?

Answer 1

This is a flow logic problem. You must use cycles to accomplish your target. "Undoing" your previous options was not defined by you, I'm guessing:
Sub DWG()
Dim ans1 As String, ans2 As String, err_msg As String
Do 'This cycle will begin and repeat when [Back] is choosen
Select Case ans1 'Undo previous operation
Case 1
ThisDrawing.Layers("PUMP_PIPING_" & size).Delete
Case "2"
ThisDrawing.Layers.Add("OMIT_PUMP_" & size).Delete
Case "3"
ThisDrawing.Layers.Add("STBP_" & size).Delete
End Select
err_msg = ""
Do 'This cycle will repeat until first answer is accepted
ans1 = InputBox(err_msg & _
"1 = STD Piping" & vbCrLf & _
"2 = Omit Pump" & vbCrLf & _
"3 = SBPP", "Pump Piping")
Select Case ans1
Case "1"
Set layerObj = ThisDrawing.Layers.Add("PUMP_PIPING_" & size)
layerObj.LayerOn = True
Case "2"
Set layerObj = ThisDrawing.Layers.Add("OMIT_PUMP_" & size)
layerObj.LayerOn = True
Case "3"
Set layerObj = ThisDrawing.Layers.Add("STBP_" & size)
layerObj.LayerOn = True
Case "" '[Cancel] button
Exit Sub
Case Else
err_msg = "Wrong Input Dude." & vbCrLf & vbCrLf
ans1 = ""
End Select
Loop While ans1 = ""
err_msg = ""
Do
ans2 = InputBox(err_msg & _
"1 = STD Louvers" & vbCrLf & _
"2 = IND louvers" & vbCrLf & _
"3 = Back ", "Pump Piping")
Select Case ans2
Case "1"
Set layerObj = ThisDrawing.Layers.Add("LOUVRES_STD")
layerObj.LayerOn = True
Case "2"
Set layerObj = ThisDrawing.Layers.Add("LOUVRES_INDUS")
layerObj.LayerOn = True
Case "3"
'Do nothing, loop control
Case "" '[Cancel] button
Exit Sub
Case Else
err_msg = "Wrong Input Dude." & vbCrLf & vbCrLf
ans2 = ""
End Select
Loop While ans2 = ""
Loop While ans2 = "3"
End Sub
Also made some changes:
Handle [Cancel] button;
Merged error messages in input box, so user doesn't have to press a lot a buttons when a mistake is done;
Made a more traditional code formatting
Part II - "Ask before doing" alternative
Sub DWG()
Dim ans1, ans2
ans1 = Choose(Val(InputBox("1 = STD Piping" & vbCrLf & "2 = Omit Pump" & vbCrLf & "3 = SBPP", "Pump Piping")), "PUMP_PIPING_", "PUMP_PIPING_", "PUMP_PIPING_")
If IsNull(ans1) Then MsgBox "Wrong Input Dude.": Exit Sub
ans2 = Choose(Val(InputBox("1 = STD Louvers" & vbCrLf & "2 = IND louvers")), "LOUVRES_STD", "LOUVRES_INDUS")
If IsNull(ans2) Then MsgBox "Wrong Input Dude.": Exit Sub
ThisDrawing.Layers.Add(ans1 & Size).LayerOn = True
ThisDrawing.Layers.Add(ans2).LayerOn = True
End Sub