Luhn test of credit card numbers: Difference between revisions

=={{header|BCPL}}==

<lang bcpl>get "libhdr"

let luhn(s) = valof

$( let sum=0 and fac=1

for i = s%0 to 1 by -1

$( unless '0' <= s%i <= '9' resultis false

sum := sum + fac*(s%i - '0') rem 10 + fac*(s%i - '0')/10

fac := 3 - fac

$)

resultis sum rem 10 = 0

$)

let show(s) be

writef("%S: %S*N", s, luhn(s) -> "pass", "fail")

let start() be

$( show("49927398716")

show("49927398717")

show("1234567812345678")

show("1234567812345670")

$)</lang>

{{out}}

<pre>49927398716: pass

49927398717: fail

1234567812345678: fail

1234567812345670: pass</pre>