VBA excel compile error : Expected Sub,Function, or property

Your problem is with the Mod operator. VBA doesn't recognize the syntax you provided.

Here is some documentation for the Mod operator - http://msdn.microsoft.com/en-us/library/se0w9esz.aspx

Th Mod operator is a binary operator and requires one left and one right argument.

You need to change

ii i Mod n   

to

ii = i Mod n

Here is the revised example you provided.

Sub Rungenkutta()


Dim Noofitrations As Integer
Dim n As Integer
Dim ii As Integer
Noofitrations = Cells(2, 10)
n = Cells(3, 10)
h = Cells(3, 4)
col = 8
x0 = Cells(col, 9)
y0 = Cells(col, 10)

For i = 1 To Noofitrations

Cells(7, 3) = x0
Cells(7, 4) = y0
xn = x0 + h
yn = y0 + Cells(18, 3)

ii = i Mod n
If ii = 0 Then
   col = col + 1
   Cells(col, 9) = xn
   Cells(col, 10) = yn
End If
x0 = xn
y0 = yn

Next


End Sub