isbn check diget

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blackcat - 06 Jan 2005 14:01 GMT

im trying to calculate the check diget for an isbn number, i know the theory
of doing this, i need to take each individual number and multiply it with a
weighting number. my problem is, i'd like to put the isbn number in as a
whole field, ie 156054021, does anyone know how to pull off each indivutual
number, ie in a loop, 1st time round pull off the 1 and * by 7, then the 5
and * by 6, then the 6, then the 0 etc.

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Tim Ferguson - 06 Jan 2005 16:44 GMT

> i'd like to put the isbn number in as a
> whole field, ie 156054021, does anyone know how to pull off each
> indivutual number, ie in a loop, 1st time round pull off the 1 and *
> by 7, then the 5 and * by 6, then the 6, then the 0 etc.

strNumber = format(dwISBN, "000000000")
for p = 1 ot len(strNumber)
wDigit = CInt(mid(strNumber,p,1))
Debug.Print wDigit
' or do something useful with it
next p

Hope that helps

Tim F

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blackcat - 07 Jan 2005 10:29 GMT

thanks, i'll give that a go

> > i'd like to put the isbn number in as a
> > whole field, ie 156054021, does anyone know how to pull off each
[quoted text clipped - 11 lines]
>
> Tim F

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blackcat - 07 Jan 2005 14:51 GMT

sorry to be a pain, but the code you gave me doesn't give me each indivual
number from the string seperatly, so that i can do a multiplication on each
seperate number, any more ideas please, thanks

> im trying to calculate the check diget for an isbn number, i know the theory
> of doing this, i need to take each individual number and multiply it with a
> weighting number. my problem is, i'd like to put the isbn number in as a
> whole field, ie 156054021, does anyone know how to pull off each indivutual
> number, ie in a loop, 1st time round pull off the 1 and * by 7, then the 5
> and * by 6, then the 6, then the 0 etc.

Reply to this Message

Tim Ferguson - 07 Jan 2005 17:47 GMT

> sorry to be a pain, but the code you gave me doesn't give me each
> indivual number from the string seperatly, so that i can do a
> multiplication on each seperate number, any more ideas please,

I am guessing that this was meant to be a response to me: it helps if you
can stick messages on the end of the thread :-)

The code I suggested does indeed shell out individual digits -- you may
want an algorithm something like this

' put in a dummy element (0) to help indexing later on
varMultiplier = Array(Null,2,3,4,2,3,4,6,7,8)

' force the number into nine digits
strNumber = format(dwISBN, "000000000")

' prepare the accumulator
dwCheckSum = 0

' shell out individual digits
for p = 1 to len(strNumber) ' always 1 to 9...

' we need a number not a char
wDigit = CInt(mid(strNumber,p,1))

' multiply it and add it in
dwCheckSum = dwCheckSum + wDigit * varMultiplier(p)

next p

Debug.print "Checksum = " & dwCheckSum

Does that not do it for you?

Tim F

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