Auto Average Cells on Either Side of Blank in Column

So this is the first ever post I have made to a forum. I am a total beginner to VBA. This is real simple I am sure. Not sure why I am getting an error, seems rather straightforward to me! I left my first attempt at average in there although at this point I am assuming that doesn't work for seem reason as current attempt. Also, is there a VBA function for average or we have to use the application average? Thanks

Sub Macro2()
' Macro2 Macro
Dim A As Long
A=100
For i = 1 To A
If Not (IsNumeric(Cells(i, 3).Value)) Then
Cells(i, 3).Value = ((Cells(i + 1, 3) + Cells(i - 1, 3))) / 2
'Cells(i, 3).Value = Application.Average(Range(Cells(i+1,3),Cells(i-1,3))
End if
Next i
End Sub

1. "IsNumeric" returns "True" if the entire expression is recognized as a number, otherwise, it returns "False".

If Not (IsNumeric(Cells(i, 3).Value)) Then = If Not True Then, where "IsNumeric(Cells(i, 3).Value)" is a Boolean.

The condition is performed only if the values are non-numeric.
"Not" in this construction is unnecessary.

"For i = 1 to 100 ... Cells(i - 1, 3).Value / 2" => Cells(1 - 1, 3).Value / 2 => Cells(0, 3).Value / 2 => Error, because there is no "0" row.

Yes, I see that it is a True or False Boolean. Turned out the issue was the zero row problem I neglected to see. Sometimes the obvious slips the mind. Thanks for the help!