ISBN13 check digit: Difference between revisions
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978-2-74839-908-0 : Good
978-2-74839-908-5 : Bad check-digit 5; should be 0
</pre>
=={{header|Phix}}==
<lang Phix>procedure check_isbn13(string isbn)
integer digits = 0, checksum = 0, w = 1
for i=1 to length(isbn) do
integer ch = isbn[i]
if ch!=' ' and ch!='-' then
ch -= '0'
if ch<0 or ch>9 then checksum = 9 exit end if
checksum += ch*w
digits += 1
w = 4-w
end if
end for
checksum = remainder(checksum,10)
string gb = iff(digits=13 and checksum=0 ? "good" : "bad")
printf(1,"%s: %s\n",{isbn,gb})
end procedure
constant isbns = {"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083",
"978-2-74839-908-0","978-2-74839-908-5","978 1 86197 876 9"}
for i=1 to length(isbns) do check_isbn13(isbns[i]) end for</lang>
{{out}}
<pre>
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad
978-2-74839-908-0: good
978-2-74839-908-5: bad
978 1 86197 876 9: good
</pre>
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