Concatenate multiple strings into single msgbox - excel

Question

via the below code I have a number of validation steps. Currently if a user omits 1 or more data inputs and or inputs incorrectly data they are getting multiple msgboxes. Not a great UI experience, what I'm looking to do is to concatenate these strings into a single msgbox. Bear in mind I'm unable to do so using System.Text etc to generate a string builder using append.
I'm relatively new to vba so if you do post any comments or feedback if you could explain it as fully as possible.
Public Function ValidateMe(strAccNum As String, iDte As Integer, strTRS As String, strPrem As String) As Boolean
' Function tests each input passed to it and validates it. If there is an issue the user is notified with a message box.
Dim blnValAcc As Boolean
Dim blnValDte As Boolean
Dim blValTRS As Boolean
Dim blnValPrem As Boolean
Dim blnValidOverall As Boolean
' Default to Invalid
blnValAcc = False
blnValDte = False
blnValTRS = False
blnValPrem = False
blnValidOverall = False
' Validate Account Number
Dim strMessage As String
Dim strSortCode As String
strMessage = ""
strSortCode = Left(strAccNum, 6)
' AccNum must be 14 characters long and all characters must be numeric
If (Len(strAccNum) = 14 And (IsNumeric(strAccNum) = True)) Then
blnValAcc = True
Else:
strMessage = strMessage & vbNewLine & "Account Number must be 14 characters long and contain only numeric characters."
End If
' 8 and 10 digit account nubmers cannot have a due date change
If (Len(strAccNum) = (8 Or 10) And (IsNumeric(strAccNum) = True)) Then
blnValAcc = False
strMessage = strMessage & vbNewLine & "8 and 10 digit account numbers cannot have a due date change."
End If
' Checks sort code against list of sort codes if the accout number has already passed previous tests
If blnValAcc = True Then
blnValAcc = CheckSortCode(strSortCode)
If blnValAcc = False Then
strMessage = strMessage & "Check sort code."
End If
End If
If blnValAcc = False Then
MsgBox strMessage, , "Check Account Number"
End If
' Validate new Due Date
If (iDte >= 1 And iDate <= 31) Then
blnValDte = True
Else:
blnValDte = False
MsgBox "Please enter a valid due date, a number between 1 and 31", , "Invalid Date"
End If
If ((strTRS = "Yes") Or (strTRS = "No")) Then
blnValTRS = True
End If
' Validate strPrem
If strPrem = "Yes" Then
blnValPrem = True
Else:
MsgBox "Customer must be advised of how change may affect premiums.", , "Premium Changes"
End If
' Validate strTRS
If strTRS = "" Then
valTRS = False
MsgBox "Please select an option from the drop down menu.", , "Customer has been advised of TRS implications?"
End If
If ((blnValAcc = True) And (blnValDte = True) And (blnValTRS = True) And (blnValPrem = True)) Then
blnValidOverall = True
End If
' Function returns true or false
ValidateMe = blnValidOverall
End Function

Answer 1

Basic pattern:
Dim msg as string
If someProblem1 then
msg = msg & iif(len(msg) > 0, vbLf, "") & "Problem1 description"
end if
if someProblem2 then
msg = msg & iif(len(msg) > 0, vbLf, "") & "Problem2 description"
end if
'etc etc
'done testing...
if len(msg) > 0 then
msgbox "There are some problems with your submission:" & vbLf & vbLf & msg,, "Oops"
end if
ValidateMe = (Len(msg) = 0)