Excel: Omitting rows/columns from VBA macro - vba

Question

With some help, I've put together two functions that will work in unison to first convert all of my data from the "text" format to a "number" format. After which it will set each column to a fixed number of characters.
The two sub-routines I'm using are listed below, but I can't figure out how to omit certain rows/columns for the respective functions.
When running the psAdd function, I want to omit the first 3 rows from the range, and for the FormatFixedNumber function I want to omit several columns. The problem with the latter is that I have 1000+ columns of data and a key header row containing a 1 or 0 that represents whether the column should be converted.
How could modify this code to skip the first 3 rows in the first sub, and several columns marked with a 0 in the second?
Sub psAdd()
Dim x As Range 'Just a blank cell for variable
Dim z As Range 'Selection to work with
Set z = Cells
Set x = Range("A65536").End(xlUp).Offset(1)
If x <> "" Then
Exit Sub
Else
x.Copy
z.PasteSpecial Paste:=xlPasteAll, Operation:=xlAdd
Application.CutCopyMode = False 'Kill copy mode
End If
x.ClearContents 'Back to normal
End Sub
Sub FormatFixedNumber()
Dim i As Long
Application.ScreenUpdating = False
For i = 1 To lastCol 'replace 10 by the index of the last column of your spreadsheet
With Columns(i)
.NumberFormat = String(.Cells(2, 1), "0") 'number length is in second row
End With
Next i
Application.ScreenUpdating = True
End Sub

Answer 1

1. First code
At the moment you are working on all the cells on a sheet with z. You can reduce this to the UsedRange - ignoring the first three rows by
forcing the UsedRange to update before using it (to avoid redunant cells)
testing if the z exceeds 3 rows
if so resize z by three rows using Offset and Resize
Sub psAdd()
Dim x As Range 'Just a blank cell for variable
Dim z As Range 'Selection to work with
ActiveSheet.UsedRange
Set z = ActiveSheet.UsedRange
If z.Rows.Count > 3 Then
Set z = z.Cells(1).Offset(3, 0).Resize(z.Rows.Count - 3, z.Columns.Count)
End If
'using Rows is better than hard-coding 65536 (bottom of xl03 - but not xl07-10)
Set x = Cells(Rows.Count,"A").End(xlUp).Offset(1)
If x <> "" Then
Exit Sub
Else
x.Copy
z.PasteSpecial Paste:=xlPasteAll, Operation:=xlAdd
Application.CutCopyMode = False 'Kill copy mode
End If
x.ClearContents 'Back to normal
End Sub
2. Second code
Run a simple test on each header cell to proceed if it doesn't equal 0. Assuming that the header cell is in row 1 then
Sub FormatFixedNumber()
Dim i As Long
Application.ScreenUpdating = False
For i = 1 To lastCol 'replace 10 by the index of the last column of your spreadsheet
If Cells(1, i) <> 0 Then
With Columns(i)
.NumberFormat = String(.Cells(2, 1), "0") 'number length is in second row
End With
End If
Next i
Application.ScreenUpdating = True
End Sub