How To Subtract CBOT Grain Prices

I had to calculate the difference between Chicago Board of Trade grain futures prices using VB.net and came up with the following (admittedly clunky) solution. It's a little tricky because CBOT prices, as posted, mix octal and decimal numbers. Anyway, here is my code for you to enjoy and tear apart:

```
Public Function GrainSubtraction(ByVal numberOne As Double, ByVal numberTwo As Double) As Double

' This is a somewhat convoluted function to subtract CBOT grain prices ... but it seems to work
' It assumes the numbers have no decimals - that is, if the price of corn is $4.75 3/4 per bushel, this number is represented as 4756 where the last digit (6) represents 6/8

' Basically, we perform octal subtraction on the smallest unit digit and regular decimal subtraction on the remaining digits
' I use arrays to do this so I can isolate each digit - there is probably a more efficient way to do this, though - I'm not a quant

Dim tempOne As Double = 0.0
Dim tempTwo As Double = 0.0

Dim inverted As Boolean = False 'Flags whether the second number is larger than the first
Dim answer As Double = 0.0 ' This will be our ultimate response
Dim multiplier As Double = 1.0

' Here, we compare the two numbers and invert them if the second number is largest then the first

If numberOne = numberTwo Then Return 0.0

If numberOne lengthTwo Then numberLength = lengthOne Else numberLength = lengthTwo

' Create our array
Dim numberOneArray(numberLength) As Integer
Dim numberTwoArray(numberLength) As Integer
Dim answerArray(numberLength) As Integer ' This will hold our answer as an array

' Set Array Values To Zero
For I = 0 To numberLength - 1
numberOneArray(I) = 0
numberTwoArray(I) = 0
Next

For I = 0 To lengthOne - 1
numberOneArray(I) = tempOne Mod 10
tempOne = Int(tempOne / 10)
Next

For I = 0 To lengthTwo - 1
numberTwoArray(I) = tempTwo Mod 10
tempTw

The following will shorten your code considerably:

Public Function GrainSubtraction(ByVal numberOne As Double, ByVal numberTwo As Double) As Double
    Dim Dec1 As Integer = CInt(Int(numberOne / 10.0))
    Dim Oct1 As Integer = CInt(numberOne - (Dec1 * 10))
    Dim Dec2 As Integer = CInt(Int(numberTwo / 10))
    Dim Oct2 As Integer = CInt(numberTwo - (Dec2 * 10))
    Dim ResultDec, ResultOct As Integer
    If Oct1 < Oct2 Then
        Dec1 -= 1
        ResultOct = CInt(7 - (Oct2 - Oct1))
    Else
        ResultOct = CInt(Oct1 - Oct2)
    End If
    ResultDec = CInt(Dec1 - Dec2)
    Return CDbl((Math.Abs(ResultDec * 10) + ResultOct) * Math.Sign(ResultDec))
End Function

This does simple octal subtraction on the last digits of the numbers supplied and decimal subtraction on the rest. I left the parameters and the return type as doubles but it would make more sense to have them as integers, since that's what they basically are.

StackExchange Code Review Q#29755, answer score: 3