Concatenate two strings into one cell - excel

Question

I have code I created with the help of the internet.
It loops through a list to find a specific string. Then it takes column B cell and pastes it onto another workbook.
But I have two different strings in the list. each time my code overwrites the first string.
I want to concatenate the two but with a comma between. e.g. [16, 5]
DATA
[C]_GA-M126_ST16_1.5_1 16
[C]_GA-M126_ST16_1.5_2 16
[C]_GA-M126_ST16_1.5_3 16
[C]_GA-M126_ST16_1.5_4 16
[C]_GA-M126_ST16_1.5_159 5
[C]_GA-M126_ST16_1.5_160 5
[C]_GA-M126_ST16_1.5_161 5
[C]_GA-M126_ST16_1.5_162 5
Sub POP_LT_UNC()
Dim W_DIP As Workbook
Dim W_PD As Workbook
Dim WDir As String
Dim CTRL As String
Dim PD_CTRL As Long
Dim nRow As Long
Dim I As Long
Dim C As Long
Dim PD_CELL As Range
Dim firstaddress As String
Dim LT_NUM As String
Dim first_LT As String
Dim ALL_LT As String
'=============================
' Set Pointer to WorkSheets
'=============================
WDir = ActiveWorkbook.Path
W_PD_DIR = WDir & ".\_database\POINT-DATA-ALL COLLECTOINS_v2.xlsx"
Set W_DIP = ThisWorkbook
Workbooks.Open (W_PD_DIR)
Set W_PD = Workbooks("POINT-DATA-ALL COLLECTOINS_v2.xlsx")
GDETrow = 17
Do Until GDETrow = 41
GDETrow = GDETrow + 1
With W_PD.Sheets(1).Range("A:A")
CTRL = W_DIP.Sheets("AFTER_SURVEY").Cells(GDETrow, 2)
Set PD_CELL = Range("A:A").Find(What:=CTRL)
If Not PD_CELL Is Nothing Then
firstaddress = PD_CELL.Address
Do
cRow = PD_CELL.Row
LT_NUM = W_PD.Sheets(1).Cells(cRow, 2)
Set PD_CELL = .FindNext(PD_CELL)
first_LT = LT_NUM
ALL_LT = first_LT & ", " & LT_NUM
W_DIP.Sheets("AFTER_SURVEY").Cells(GDETrow, 19) = ALL_LT
Loop While Not PD_CELL Is Nothing And PD_CELL.Address <> firstaddress
End If
End With
Loop
W_PD.Close
End Sub

Answer 1

Assuming W_DIP.Sheets("AFTER_SURVEY").Cells(GDETrow, 19) = ALL_LT is the line where the text is written, you can to this:
Dim rangeToChange as Excel.Range
Set rangeToChange = W_DIP.Sheets("AFTER_SURVEY").Cells(GDETrow, 19)
If IsEmpty(rangeToChange.Value2) Then
rangeToChange.Value2 = ALL_LT
Else 'already text in the Cell, add value with comma
rangeToChange.Value2 = rangeToChange.Value2 & ", " & ALL_LT
End If
Just replace the Line above with the Code provided.
This will fill the Cell with the value provided and only add the comma if there already is value inside the Cell.
.Value2 is used to avoid an implicit call to the default property of the cell.