i found this code by pressing screenupdating in the help section of vba. it
doesn't work. it says i is undefined. so i write dim i as integer. then it
says starttime is undefined.

Dim elapsedTime(2)
Application.screenupdating = True

For i = 1 To 2
If i = 2 Then Application.screenupdating = False
startTime = Time
Worksheets("Sheet1").Activate
For Each c In ActiveSheet.Columns
If c.Column Mod 2 = 0 Then
c.Hidden = True
End If
Next c
stopTime = Time
elapsedTime(i) = (stopTime - startTime) * 24 * 60 * 60
Next i
Application.screenupdating = True
MsgBox "Elapsed time, screen updating on: " & elapsedTime(1) & _
" sec." & Chr(13) & _
"Elapsed time, screen updating off: " & elapsedTime(2) & _
" sec."