Solved Problem when comparting floating values (1 Viewer)

[Teggun]

Hi guys, I'm having a problem when trying to compare two floating values, and I have no idea what happens here, I hope someone can help me out with this.

What I need is to compare a value stored in a table (set up as a double on it) with a operation done, and return true or false if it is the same. What happens is that when I do so, even the value being showed as equal in the debugger, it still sends it wrong to me.

'//Setting variables.
Dim rsStock As Recordset
Dim bRecord As Double
Dim bIn As Double
Dim bOut As Double
Dim bCurrent As Double


'//Setting the recordset.
Set rsStock = CurrentDb.OpenRecordset("SELECT tblStock.* FROM tblStock ORDER BY [tblStock]![Date]", dbOpenDynaset)
rsStock.MoveFirst

bCurent = 0

'//Loop through all records to check if the balance is correct at all records.
While Not rsStock.EOF = True
    '//Capturing value from record.
    bRecord = rsStock.Fields("Balance")
    
    '//Making operation to get correct value.
    If rsStock.Fields("In") > 0 Then
        bIn = rsMStock.Fields("In")
        bCurrent = Round(bCurrent + bIn, 2)
    End If
    
    If rsStock.Fields("Out") > 0 Then
        bOut = rsMStock.Fields("Out")
        bCurrent = Round(bCurrent - bOut, 2)
    End If
    
    '//Checking if the value in table is equal to the operation made in the loop.
    If bCurrent <> bRecord Then
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Wrong!]"
    Else
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Correct!]"
    End If
    
    rsStock.MoveNext
    
Wend

rsStock.Close
Set rsStock = Nothing

I don't understand what is wrong, everything working nicely but even the values being the same, still randomly shows "Wrong!" in a lot of cases. In the debugger shows something like this:

(159) [9,47/9,47] [Correct!]
(261) [12,1/12,1] [Wrong!]
(407) [89,6/89,6] [Correct!]
(610) [82,37/82,37] [Wrong!]
(650) [79,29/79,29] [Wrong!]
(669) [76,17/76,17] [Wrong!]
(1525) [73,5/70,82] [Wrong!]
(1521) [70,82/73,49] [Wrong!]
(1527) [68,96/68,96] [Correct!]

If any of you could help me with this it would be higjly appreciated. Thanks in advance.

 

[theDBguy]

Hi. Try this on a separate test database, convert your Double fields into Currency and then try your code again to see if it makes any difference and let us know.

 

[CJ_London]

doubles are inexact at a very small level which is why you sometimes don't get a match. You may not be seeing it because you have formatted to show perhaps 2 decimal places for your balance field. With formatting, the underlying value remains unchanged

 

[Teggun]

Thanks for you answers guys, I actually did manage to sove it by rounding the value in the comparation condition. I guess this makes that inexactity deisappear.

If Round(bCurrent, 2) <> Round(bRecord, 2) Then
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Wrong!]"
Else
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Correct!]"
End If

 

[theDBguy]

Thanks for you answers guys, I actually did manage to sove it by rounding the value in the comparation condition. I guess this makes that inexactity deisappear.

If Round(bCurrent, 2) <> Round(bRecord, 2) Then
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Wrong!]"
Else
        Debug.Print "(" & rsMStock.Fields("IDStock") & ") [" & bCurrent & "/" & bRecord & "] [Correct!]"
End If

Hi. Glad to hear you got it sorted out. Good luck with your project.

 

[CJ_London]

no need to round bCurrent - you've already done that in your code

 

[Pat Hartman]

Unless you need more than four decimal places, you might consider changing the data type from double to currency. Currency is both a data type and a format so just because you use the currency data type doesn't mean you have to format the field as currency. Percent, Standard, and the other formats work equally.

The Currency data type is a scaled integer which is why it doesn't have the imprecision of floating point since it is always "rounded" to four decimal places.

Keep in mind that formatting should not be applied at the table level because it obfuscates the actual value as you are seeing. Apply your formats on forms and reports and maybe queries that humans will see. Humans never see your tables so don't format them for human viewing.

 

[WayneRyan]

Tegun,

Floating point numbers are not good at all.
They can't give an EXACT rendition of some very simple numbers.
The part to the right of the decimal point is made up by adding (1/2, 1/4, 1/8 ...) for a finite
number of bits. Even with double precision there's numbers it can't do (like ... 1.4 maybe?).

As Pat and CJ mentioned you can use the currency type.
For other applications you can use the Decimal datatype and size it to your desired precision
on both the left/right of the decimal; Decimal(9,5) <-- number like 9999.99999

Anyway, what I'm really wanting to say is that CODE is a 4-letter word. Try to avoid it.

SQL is a very nice 3-letter word:

Select IDStock, 
       Sum(In) as SumIn,
       Sum(Out) as SumOut,
       Abs(Sum(In) - Sum(Out)) As Delta  ' Calculate difference of sums
From   tblStock
Group by IDStock
Having Abs(Sum(In) - Sum(Out)) > 0.02    ' Just For Fun, only show accts > 2 cents
Order By Abs(Sum(In) - Sum(Out)) Desc    ' Show "worst" first; need to repeat calculation
                                         ' because it won't understand --> "SumIn" or "SumOut"

You can save that as a query and have 0 code.

hth,
Wayne

 

[Teggun]

Unless you need more than four decimal places, you might consider changing the data type from double to currency. Currency is both a data type and a format so just because you use the currency data type doesn't mean you have to format the field as currency. Percent, Standard, and the other formats work equally.

The Currency data type is a scaled integer which is why it doesn't have the imprecision of floating point since it is always "rounded" to four decimal places.

Keep in mind that formatting should not be applied at the table level because it obfuscates the actual value as you are seeing. Apply your formats on forms and reports and maybe queries that humans will see. Humans never see your tables so don't format them for human viewing.

Thanks a lot, actually changing it to currency also worked, I'll keep this tip in mind from now on. Did not know about this problem with floating numbers.

Tegun,

Floating point numbers are not good at all.
They can't give an EXACT rendition of some very simple numbers.
The part to the right of the decimal point is made up by adding (1/2, 1/4, 1/8 ...) for a finite
number of bits. Even with double precision there's numbers it can't do (like ... 1.4 maybe?).

As Pat and CJ mentioned you can use the currency type.
For other applications you can use the Decimal datatype and size it to your desired precision
on both the left/right of the decimal; Decimal(9,5) <-- number like 9999.99999

Anyway, what I'm really wanting to say is that CODE is a 4-letter word. Try to avoid it.

SQL is a very nice 3-letter word:

Select IDStock,
       Sum(In) as SumIn,
       Sum(Out) as SumOut,
       Abs(Sum(In) - Sum(Out)) As Delta  ' Calculate difference of sums
From   tblStock
Group by IDStock
Having Abs(Sum(In) - Sum(Out)) > 0.02    ' Just For Fun, only show accts > 2 cents
Order By Abs(Sum(In) - Sum(Out)) Desc    ' Show "worst" first; need to repeat calculation
                                         ' because it won't understand --> "SumIn" or "SumOut"

You can save that as a query and have 0 code.

hth,
Wayne

Thanks! I'll keep that in mind. Actually this is only a macro to check for errors in the table so it might not be running always, anyways it's good to learn new things!

 

[Pat Hartman]

There's an interesting article, among many, at www.fmsinc.com. I think its title is "When Access math doesn't add up" There are also useful samples and software.