Luhn test of credit card numbers: Difference between revisions

=={{header|Action!}}==

<lang Action!>PROC ReverseDigits(CHAR ARRAY n,rev)

BYTE i,j

i=n(0)

WHILE i>0 AND n(i)='0

DO

i==-1

OD

j=1

WHILE i>0

DO

rev(j)=n(i)

j==+1 i==-1

OD

rev(0)=j-1

RETURN

BYTE FUNC SumOddDigits(CHAR ARRAY n)

BYTE sum,i

sum=0

FOR i=1 TO n(0) STEP 2

DO

sum==+ValB(n(i))

OD

RETURN(sum)

BYTE FUNC SumEvenDigitsMultiplied(CHAR ARRAY n)

BYTE sum,i,v

sum=0

FOR i=2 TO n(0) STEP 2

DO

v=ValB(n(i))*2

IF v>9 THEN v==-9 FI

sum==+v

OD

RETURN(sum)

BYTE FUNC Luhn(CHAR ARRAY n)

CHAR ARRAY rev(20)

BYTE s1,s2

ReverseDigits(n,rev)

s1=SumOddDigits(rev)

s2=SumEvenDigitsMultiplied(rev)

IF (s1+s2) MOD 10=0 THEN

RETURN(1)

FI

RETURN(0)

PROC Test(CHAR ARRAY n)

PrintF("%S is ",n)

IF Luhn(n) THEN

PrintE("valid")

ELSE

PrintE("invalid")

FI

RETURN

PROC Main()

Test("49927398716")

Test("49927398717")

Test("1234567812345678")

Test("1234567812345670")

RETURN</lang>

{{out}}

[https://gitlab.com/amarok8bit/action-rosetta-code/-/raw/master/images/Luhn_test_of_credit_card_numbers.png Screenshot from Atari 8-bit computer]

<pre>

49927398716 is valid

49927398717 is invalid

1234567812345678 is invalid

1234567812345670 is valid

</pre>