How do I convert VB's Double to COBOL's COMP-3?

Question

Hi All,

Does anyone here know how to convert a VB Double to Cobol S9(15)V99 Comp-3 data type. Any help would be appreciated.

Answer 1

Does it need to be done in the same program? It seems to me it would be easier to find a common format that both VB and COBOL can understand.

That would be ... TEXT ! Yes, is it an option to write the code out to a file as text "3.14159" and have the COBOL code read it in in that format and MOVE it to the comp-field?

If that's not possible, the COMP-3 is a fairly simple BCD type. I would convert the number to a string anyway then take it two characters at a time into a byte array.

The S9(15)V99 requires 18 nybbles (a nybble being 4 bits, or half an octet) to store:

• one for the sign.
• 15 for the integer bit.
• 2 for the non-integer bit (V is an implied decimal, not a real one).

So the number 3.14 would be represented as the bytes:

00 00 00 00 00 00 00 31 4C

The only tricky bit is that final sign nybble (C for positive and D for negative).

Here's a bit of code I whipped up in Excel VBA (I don't have VB installed on this machine unfortunately) that shows you how to do it. The makeComp3() function should be easily transferred into a real VB program.

The macro test program outputs the values 0, 49 and 76 which are hex 00, 31 and 4C respectively (00314C is +3.14).

Option Explicit

' makeComp3. '
'   inp is the double to convert. '
'   sz is the minimum final size (with sign). '
'   frac is the number of fractional places. '

Function makeComp3(inp As Double, sz As Integer, frac As Integer) As String
    Dim inpshifted As Double
    Dim outstr As String
    Dim outbcd As String
    Dim i As Integer
    Dim outval As Integer
    Dim zero As Integer
    zero = Asc("0")

    ' Make implied decimal. '
    inpshifted = Abs(inp)
    While frac > 0
        inpshifted = inpshifted * 10
        frac = frac - 1
    Wend
    inpshifted = Int(inpshifted)

    ' Get as string and expand to correct size. '
    outstr = CStr(inpshifted)
    While Len(outstr) < sz - 1
        outstr = "0" & outstr
    Wend
    If Len(outstr) Mod 2 = 0 Then
        outstr = "0" & outstr
    End If

 

    ' Process each nybble pair bar the last. '
    outbcd = ""
    For i = 1 To Len(outstr) - 2 Step 2
        outval = (Asc(Mid(outstr, i)) - zero) * 16
        outval = outval + Asc(Mid(outstr, i + 1)) - zero
        outbcd = outbcd & Chr(outval)
    Next i

    ' Process final nybble including the sign. '    
    outval = (Asc(Right(outstr, 1)) - zero) * 16 + 12
    If inp < 0 Then
        outval = outval + 1
    End If

    makeComp3 = outbcd & Chr(outval)
End Function

Sub Macro1()
    Dim i As Integer
    Dim cobol As String

    cobol = makeComp3(3.14159, 6, 2)
    For i = 1 To Len(cobol)
        MsgBox CStr(Asc(Mid(cobol, i)))
    Next i
End Sub

Answer 2

Hi,

I wanted the conversion to be done in VB but don't know how. Anywayz thanks for the reply. Well is there anyway to code the conversion in VB? what the program does is that it reads a string input and then convert the numeric digits to COMP-3 in cobol and store it to a text file.

Answer 3

Hi,

Thank you so much. I think it worked, but when I try to upload it in the mainframe thru ftp and open it on a copy book the field value is INVALID. I think the problem is during the upload.