How to make a loop that deletes rows that contain previous dates - excel

Question

I'm creating a loop that is supposed to find cells that have dates before 01/01/2019 and if they find they delete the entire row.
The problem is that if they delete per example row number 2, the code is passing to row 3, but since row 2 was deleted previously the original row 3 would be skipped.
I wrote the loop and tried to add "i = 1 - 1" but the excel never stops running the code and blocks the program
Dim ws As Worksheet
Dim Ldate As Date
Dim N As Long
Ldate = "01/01/2019"
N = ws.Cells(Rows.Count, 8).End(xlUp).Offset(0, 0).Row
For i = 1 To N
If ws.Cells(i, 8).Value < Ldate Then
ws.Rows(i).Delete
' i = 1 - 1
End If
Next i

Answer 1

Don't let Excel guess if this string "01/01/2019" is mm/dd/yyyy or dd/mm/yyyy Never use strings to write a date, instead always use real dates: Ldate = DateSerial(2019, 1, 1) to create dates. String-Dates are very evil! The only use case to cast a real date into a string is to print it on paper or screen. All other cases must use real dates (number formats) to be reliable.
.Offset(0, 0) is usless remove it. Moving 0 rows and 0 columns from current cell will not change current cell at all.
If you delete/add rows then your loops must be backwards in order to row count correctly: For iRow = LastRow To 1 Step - 1
So you end up with something like this
Dim ws As Worksheet
Set ws = ThisWorkbook.Worksheets("Sheet1")
Dim Ldate As Date
Ldate = DateSerial(2019, 1, 1)
Dim LastRow As Long
LastRow = ws.Cells(ws.Rows.Count, 8).End(xlUp).Row
Dim iRow As Long
For iRow = LastRow To 1 Step - 1
If ws.Cells(iRow , 8).Value < Ldate Then
ws.Rows(iRow).Delete
End If
Next iRow
Alternative if you use a forward loop, you need to collect the rows to delete in a Range variable and delete it at once after the loop is finished. This way deleting doesn't affect the row counting inside the loop (because we delete after the loop):
Dim ws As Worksheet
Set ws = ThisWorkbook.Worksheets("Sheet1")
Dim Ldate As Date
Ldate = DateSerial(2019, 1, 1)
Dim LastRow As Long
LastRow = ws.Cells(ws.Rows.Count, 8).End(xlUp).Row
Dim RowsToDelete As Range
Dim iRow As Long
For iRow = 1 To LastRow
If ws.Cells(iRow , 8).Value < Ldate Then
If RowsToDelete Is Nothing Then
Set RowsToDelete = ws.Rows(iRow)
Else
Set RowsToDelete = Union(RowsToDelete, ws.Rows(iRow))
End If
End If
Next iRow
If Not RowsToDelete Is Nothing Then
RowsToDelete.Delete
End If
Actually this approach should be faster because it only performs one delete action in the end (instead of one per deleted row).
Edit according comments:
Test if a worksheet exists before you use it.
Option Explicit
Function WorksheetExists(ByVal WorksheetName As String, Optional ByVal InWorkbook As Workbook) As Boolean
'default workbook is ThisWorkbook
If InWorkbook Is Nothing Then
Set InWorkbook = ThisWorkbook
End If
Dim ws As Worksheet
On Error Resume Next
Set ws = InWorkbook.Worksheets(WorksheetName)
On Error GoTo 0
WorksheetExists = Not ws Is Nothing
End Function
Then use it like
If WorksheetExists("Sheet1") Then …
'or to test for a worksheet in a different workbook
If WorksheetExists("Sheet1", Workbooks("OtherWorkbook.xlsx")) Then

Answer 2

The simplest way is to change
For i = 1 To N
to
For i = N To 1 step -1
This way when your row is deleted it will not change the number of the following rows as these will be lower numbered rows.