My VBA code for integration (Simpson's Rule)

Sub Simpson()
Sheets("Sheet3").Select
Dim integral As Double, delta As Double, start As Double, last As Double
Dim n As Integer
start = 0
n = 20
last = 1
delta = (last - start) / n
integral = 0
For i = 1 To n / 2
integral = integral + (delta / 3) * (fval(start + (2 * i - 2) * delta) + 4 * fval(start + (2 * i - 1) * delta) + fval(start + 2 * i * delta))


Next
Cells(1, 1) = integral
End Sub