ISBN13 check digit: Difference between revisions

=={{header|CLU}}==

<lang clu>isbn13_check = proc (s: string) returns (bool)

if string$size(s) ~= 14 then return(false) end

if s[4] ~= '-' then return(false) end

begin

check: int := 0

for i: int in int$from_to(1, 14) do

if i=4 then continue end

d: int := int$parse(string$c2s(s[i]))

if i=2 cor (i>4 cand i//2=1) then d := d*3 end

check := check + d

end

return(check//10 = 0)

end except when bad_format:

return(false)

end

end isbn13_check

start_up = proc ()

po: stream := stream$primary_output()

tests: array[string] := array[string]$

["978-1734314502",

"978-1734314509",

"978-1788399081",

"978-1788399083"]

for test: string in array[string]$elements(tests) do

stream$puts(po, test)

stream$puts(po, ": ")

if isbn13_check(test)

then stream$putl(po, "good")

else stream$putl(po, "bad")

end

end

end start_up</lang>

{{out}}

<pre>978-1734314502: good

978-1734314509: bad

978-1788399081: good

978-1788399083: bad</pre>