Question

write C# console app No arrays

Credit card validation Problem. A credit card number must be between 13 and 16 digits. It must start with: –4 for visa cards –5 for mater cards –37 for American express cards –6 for discover cards •Consider a credit card number 4380556218442727 •Step1: double every second digit from right to left. If doubling of a digit results in a two-digit number, add up the two digits to get a single-digit number. •Step2: now add all the single digit numbers from step1 4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 •Step3: add all digits in the odd places from right to left in the card number 7+ 7 + 4 + 8 + 2 + 5 + 0 + 3 = 36 •Step4: sum the results from step 2 and step 3 37 + 36 = 73 •Step 5: if the results from step 4 is divisible by 10, the card number is valid; otherwise, it is invalid. In this case, the card number is not valid – because 75 not divisible by 10. use modulus operator

Answer 1

using System;
using System.Linq;
using System.Text;
using System.IO;

namespace SO
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] cards = new string[] {
                "378282246310005",
                "4012888888881881",
                "6011111111111117",
                "4222222222222",
                "76009244561",
                "5019717010103742",
                "6331101999990016",
                "30569309025904",
                "5147004213414803",
                "6011491706918120",
                "379616680189541",
                "4916111026621797",
            };
            foreach (string card in cards)
            {
                Console.WriteLine(IsValid(card));
            }
            Console.ReadLine();
        }

        public static bool IsValid(object value)
        {
            if (value == null)
            {
                return true;
            }
            string ccValue = value as string;
            if (ccValue == null)
            {
                return false;
            }
            ccValue = ccValue.Replace("-", "");
            ccValue = ccValue.Replace(" ", "");
            int checksum = 0;
            bool evenDigit = false;
            foreach (char digit in ccValue.Reverse())
            {
                if (digit < '0' || digit > '9')
                {
                    return false;
                }

                int digitValue = (digit - '0') * (evenDigit ? 2 : 1);
                evenDigit = !evenDigit;

                while (digitValue > 0)
                {
                    checksum += digitValue % 10;
                    digitValue /= 10;
                }
            }

            return (checksum % 10) == 0;
        }
    }
}