A bug I can't seem to spot, faulty logic?

Problem description: Take a stack of coins all heads up. Upturn the topmost coin and then proceed: take the top 2 coins and upturn as a single stack (tail, head becomes when upturned and placed back on the stack tail, head (the two coins are flipped as if glued together)). Now in the same way flip the top 3 coins and place back on the stack (you get: tail, tail, head (and if there were 4 coins that would be tail, tail, tail, head). When you upturn the whole stack begin again with the first coin. Continue until you return to a stack with all heads up.

(Hope that's clear)

Can anybody see why this small program should fail? The example for me where I first notice an error is when count reaches 18 with a stack of 6 coins.

I placed a button on a spreadsheet and call FlippingCoins...

Sub FlippingCoins()
Call theStackOfCoins
Call theFlipping
End Sub


Sub theStackOfCoins()
Worksheets("Sheet3").Cells(1, 3).Select
Columns("A:b").Select
Selection.ClearContents
Range("a3").Select

Dim StackOfCoins As Integer
    StackOfCoins = Worksheets("Sheet3").Cells(1, 3).Value

Dim row As Integer
    row = 0

For theStack = 1 To StackOfCoins
    Worksheets("Sheet3").Cells(row + theStack, 1).Value = True
Next theStack

End Sub

Sub theFlipping()

Dim middleCoin As Integer
    middleCoin =开发者_运维百科 0
Dim passes As Integer
    passes = 0
Dim Fst As Integer
    Fst = 0
Dim Lst As Integer
    Lst = 0

Dim stack As Integer
    stack = Worksheets("Sheet3").Cells(1, 3).Value

Dim Flip_x_coins As Integer
    Flip_x_coins = 0

Dim count As Integer
    count = 0

Dim Finished As Boolean
    Finished = False

Reset:
    Flip_x_coins = 1
For Flip_x_coins = 1 To stack
    Worksheets("Sheet3").Cells(1, 4).Value = Flip_x_coins
    count = count + 1
    If Flip_x_coins = 1 Then
        Worksheets("Sheet3").Cells(1, 1).Value = Not (Worksheets("Sheet3").Cells(1, 1).Value)
    Else
        passes = Int(Flip_x_coins) / 2
        Fst = 1
        Lst = Flip_x_coins
        For pass = 1 To passes
            If Worksheets("Sheet3").Cells(Fst, 1).Value = Worksheets("Sheet3").Cells(Lst, 1).Value Then
                    Worksheets("Sheet3").Cells(Fst, 1).Value = Not (Worksheets("Sheet3").Cells(Fst, 1).Value)
                    Worksheets("Sheet3").Cells(Lst, 1).Value = Not (Worksheets("Sheet3").Cells(Lst, 1).Value)
            End If
            Fst = Fst + 1
            Lst = Flip_x_coins - 1
        Next pass
        If Flip_x_coins Mod 2 > 0 Then
            middleCoin = (Flip_x_coins + 1) / 2
            Worksheets("Sheet3").Cells(middleCoin, 1).Value = Not (Worksheets("Sheet3").Cells(middleCoin, 1).Value)
        End If
    End If
    For testComplete = 1 To stack
        If Worksheets("Sheet3").Cells(testComplete, 1).Value = False Then
            Finished = False
            Exit For
        Else
            Finished = True
        End If
    Next testComplete
    Worksheets("Sheet3").Cells(1, 2).Value = count
If Finished = True Then
    Exit For
End If
    MsgBox "Next."
    If Flip_x_coins = stack Then
        GoTo Reset
    End If
Next Flip_x_coins

End Sub

Thanks in advance

Regards

---

In the For pass = 1 To passes loop, Lst = Flip_x_coins - 1 is wrong.

It should be: Lst = Lst - 1

On pass 18 with 6 coins, the macro compares rows 1 and 6 followed by rows 2 and 5 followed by rows 3 and 5. Obviously the last comparison should be between rows 3 and 4 instead.

I hope this isn't homework because there are lots of other problems with the macro. For example:

• no Option Explicit at the start of the macro. This has allowed you to use three variables which you haven't declared - theStack, pass, testComplete
• incorrect rounding. Given that Flip_x_coins is of Integer type, passes = Int(Flip_x_coins) / 2 is nonsense. Try passes = Int(Flip_x_coins / 2) instead
• using Goto is generally a bad idea. It has some use in VBA for error handling but, in this case, you could easily use a Do Until finished ... Loop construct instead

---

I suspect this

            Fst = Fst + 1
            Lst = Flip_x_coins - 1
        Next pass

should be

            Fst = Fst + 1
            Lst = Lst - 1
        Next pass

---

Sub Flip()

    Dim rw As Range
    Dim numCoins As Integer
    Dim iCoins As Integer, iCoin As Integer, flipCoins As Integer
    Dim v
    numCoins = 6

    Set rw = Sheet1.Range("B2").Resize(1, numCoins) 'all start as "TRUE"
    rw.Value = True

    Do
        For flipCoins = 1 To numCoins
            For iCoin = 1 To numCoins
                If iCoin <= flipCoins Then
                    v = Not rw.Cells(flipCoins - (iCoin - 1)).Value
                Else
                    v = rw.Cells(iCoin).Value
                End If
                rw.Offset(1, 0).Cells(iCoin).Value = v
            Next iCoin
            Set rw = rw.Offset(1, 0)
            rw.EntireRow.Cells(1).Value = "Flipped " & flipCoins

            If Application.CountIf(rw, "FALSE") = 0 Then
                Debug.Print "All Heads at row " & rw.Row
                Exit Do
            End If
       Next flipCoins
   Loop While rw.Row < 1000 'don't go on for ever...
End Sub