Validate Credit Card Formula in Iphone App

Answer 1

If you are selling things from inside your app, it is very likely that apple will reject it unless you are using in-app sales (in which case, you shouldn't need any credit card validation).

Answer 2

Here is some code that will likely work (uses the Luhn Algorithm):

-(BOOL) validateCardNumber:(NSString *)cardNumber
{

const char *str = [cardNumber UTF8String];
int n, i, alternate, sum;

n = strlen(str);

if ( n < 13 || n > 19 )
    return NO;

for ( alternate = 0, sum = 0, i = n-1; i>-1; –i) {
    if ( !isdigit(str[i]))
        return NO;

    n = str[i] – ‘0′;

    if ( alternate ) {
        n*=2;
        if ( n > 9 )
            n = ( n % 10 ) + 1;
    }

    alternate = !alternate;

    sum += n;
}

return ( sum % 10 == 0 );
}

Credit to Donald Bellenger for this method.

Answer 3

I was able to answer my own question, shared it above in the "updated" area.