Luhn test of credit card numbers: Difference between revisions

=={{header|GAP}}==

<lang gap>IsLuhn := function(n)

local c, d, i, j, r;

d := "0123456789";

j := 1;

r := 0;

for c in Reversed(String(n)) do

i := Position(d, c);

if i = fail then

continue;

fi;

i := j*(i - 1);

r := r + QuoInt(i, 10) + RemInt(i, 10);

j := 3 - j;

od;

return RemInt(r, 10) = 0;

end;

List([49927398716, 49927398717, 1234567812345678, 1234567812345670], IsLuhn);

# [ true, false, false, true ]</lang>