CODEWITHSUNDEEP
javastringluhn
R2S
R2S

Reputation: 1

Credit Card Validation in Java with Luhn Algorithm with a string

I'm trying to create a method to validate a credit card number, but we have to process it as a string

heres some information about my task...

Credit card numbers follow certain patterns. A credit card must have between 13 and 16 digits.

In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine if a card number is entered correctly or if a credit card is scanned correctly by a scanner. Almost all credit card numbers are generated following this validity check, commonly know as the Luhn check or the Modulus 10 check, which can be described as follows. For illustration, consider the card number 4388576018402625.

Double every second digit from right to left. If doubling of a digit results in a 2-digit number, add up the two digits to get a single-digit number. 2 x 2 = 4

2 x 2 = 4

4 x 2 = 8

1 x 2 = 2

6 x 2 = 12 (1+2= 3)

5 x 2 = 10 (1+0= 1)

8 x 2 = 16 (1+6= 7)

4 x 2 = 8

Add all the single digit numbers from step 1 4 + 4 +8 + 2 +3 + 1 + 7 + 8 = 37

Add all digits in the odd places from right to left in the card number

5 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 37

Sum the results from step 2 and step 3 37 + 37 = 74

If the result from step is divisible by 10, the card number is valid; otherwise, it’s invalid. For example, the number 4388576018402625 is invalid, but the number 4388576018410707 is a valid Visa card; the number 6011000593748745 is invalid, but the number 6011000593748746 is a valid Discover card.

here's what I have so far

static void CreditCardValidator() {
    System.out.println("enter a credit card number");
    String temp = options.nextLine();

    if (temp.length() < 13 || temp.length() > 16) {
        System.out.println("Input is invalid");
    }

    // inside loop with char at command do all the math
    int tmpdouble;
    int sum = 0;
    int counter = temp.length() - 1;
    for (int i = temp.length(); i != 0; i--) {
        char tmp = temp.charAt(i);
        //tmp converted to int
        tmpdouble = tmp * 2;

        int firstDigit;
        int secondDigit;
        if (tmpdouble >= 10) {
            firstDigit = i / 10;
            secondDigit = i % 10;
            sum = sum + firstDigit + secondDigit;
        }

        else if(tmpdouble <= 9) {
            sum = sum + tmpdouble;
        }

    HELP HERE{
        // need to have it do the same thing as above but for odd numbers
    }

where do I go from there? ^^

Thanks

Upvotes: 0

Views: 2397

Answers (1)

dom farr
dom farr

Reputation: 4181

Don't roll your own. This algorithm is already provided via commons.

https://commons.apache.org/proper/commons-validator/apidocs/org/apache/commons/validator/routines/CreditCardValidator.html

Upvotes: 2

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