Using Lookup Function

I just wanted to use lookup function in my code. But I had to re-write my for..next statement 8 times. How can I state it in one single lookup function used in a for..next statement. Here is my code

Sub iteration(r)
Dim i As Integer
Dim j As Integer
Dim x1(4) As Double
Dim arra(8, 2) As Double
Dim arrb(8, 4) As Double
r(1) = Worksheets("sonuc"). Range("j4").Value
r(2) = Worksheets("sonuc").Range("j6").Value
Dim myRange As Range
Set myRange = Worksheets("giderler").Range("b6:b11")
x1(1) = Application.WorksheetFunction.Floor(r(1), 0.5)
x1(2) = Application.WorksheetFunction.Ceiling(r(1), 0.5)
x1(3) = Application.WorksheetFunction.Floor(r(2), 0.5)
x1(4) = Application.WorksheetFunction.Ceiling(r(2), 0.5)
For i = 1 To 4