sub will not loop through second if statement vba - vba

Question

Really hope someone out there can help me. So i have the following code. The independent codes work fine by themself, but when executing the script, it only loops through the first condition. What i want it to do is to loop through all the code, each time. I think it's a small thing I am missing, but i can't seem to find a solution.
Sub Copypre()
Dim i As Integer
Dim n As Integer
For i = 2 To 10
'Checks the number of entries in the "Pre" table, to make sure that there are no spaces between the lines
On Error Resume Next
n = Worksheets("Pre").Range("A2:A6000").Cells.SpecialCells(xlCellTypeConstants).Count
If n = Null Then
n = i
'Goes through the different sheets to find all "pre" values and paste them in the "Pre" sheet
If ThisWorkbook.Sheets("273").Range("A" & i).Value = "Pre" Then
Range(Cells(i, 1), Cells(i, 3)).Select
Selection.Copy
Sheets("Pre").Select
Range("A" & n).Select
ActiveSheet.Paste
Sheets("2736").Select
End If
End If
Next i
End Sub

Answer 1

There are a couple of issues with your code, but the main issue may be that If n = Null will never be true since an integer cannot be Null. You could change this to If n = 0.
A couple of things to consider:
Error handling: Always go back to normal error handling with On Error GoTo 0 as soon as possible. This way you would have known (assuming that there is no sheet "2736" in your workbook) that your code is trying to select a sheet that does not exist.
Range argument: Be carefull when not specifying the sheet when using the Range (and Cells) argument. When you switch back and fourth between different sheets that you select, there is a change that you may loose track of what sheet the Range is returning data from. Consider declaring each worksheet and then copy your ranges like:
Dim w273 As Worksheet
Set w273 = ThisWorkbook.Sheets("273")
w273.Range(w273.Cells(i, 1), w273.Cells(i, 3)).Copy

Answer 2

Loops can quickly consume time with long columns of data and I suspect that your code was heavily redacted. Try this alternate method of block copying across to the destination worksheet.
Sub Copypre()
With Sheets("273").Cells(1, 1).CurrentRegion
.AutoFilter
.Columns(1).AutoFilter field:=1, Criteria1:="=Pre"
If CBool(Application.Subtotal(103, .Offset(1, 0))) Then
.Offset(1, 0).Resize(, 3).Copy _
Destination:=Sheets("Pre").Cells(Rows.Count, 1).End(xlUp).Offset(1, 0)
End If
.AutoFilter
End With
End Sub
All that can get accomplished without a single variable declaration.
Addendum:
As to your original question, the whole if "pre"/copy/paste section is nested within the if n = Null so it can only be reached if n = Null is true. If there are no .SpecialCells(xlCellTypeConstants)to count, n will be assigned its default value (e.g. 0). Zero is not equal to Null so that condition is never met. To check your code, add the following line.
On Error Resume Next
n = Worksheets("Pre").Range("A2:A6000").Cells.SpecialCells(xlCellTypeConstants).Count
Debug.Print "n is " & n
After running it, open the Immediate window with Ctrl+G. If there are no non-formula values in Pre!A2:A6000 you should see n is 0.

Answer 3

Thanks allot for all the advices. The null trick worked! I am totally new to VBA so it's nice to get some tips and tricks from experts. I will try to make the code more simple as Jeeped mentioned, as this is not very elegant. In regards to the sheets, i can totally understand the confusion, i have fixed that also. It works now and looks like this:
Sub Copypre()
Dim i As Integer
Dim n As Integer
For i = 2 To 5000
' Checks the number of entries in the "Pre" table, to make sure that there are no spaces between the lines
On Error Resume Next
n = Worksheets("Pre").Range("A2:A6000").Cells.SpecialCells(xlCellTypeConstants).Count
' Goes through the different sheets to find all pre values and paste them in the "Pre" sheet
If ThisWorkbook.Sheets("2736").Range("A" & i).Value = "Pre" Then
Sheets("2736").Select
Sheets("2736").Range(Cells(i, 1), Cells(i, 3)).Select
Selection.Copy
Sheets("Pre").Select
Range("A" & (n + 2)).Select
ActiveSheet.Paste
Sheets("2736").Select
Sheets("2736").Select
Range(Cells(i, 5), Cells(i, 6)).Select
Selection.Copy
Sheets("Pre").Select
Range("E" & (n + 2)).Select
ActiveSheet.Paste
Sheets("2736").Select
End If
Next i
End Sub