Apologies I should have tested it, there were two problems. 1st too many "R" s in "inarrr" and secondly the .value extension is not valid for a variatn arry I only changed one of them
I have also tweaked your code to shoe you how to use only one index (i) instead of i, R and C

Sub test()Dim i As Long
Dim inarr As Variant
inarr = Range(Cells(1, 1), Cells(9, 6))


For i = 1 To 9
    If i <= 5 Then
    inarr(i, i) = "*"
Else
    inarr(i, 10 - i) = "*"
    End If
Next i




Range(Cells(1, 1), Cells(9, 6)) = inarr