/*Programmer Steven Brown

Date: Start May18 - End May22

Card Number

Description: To demonstrate how to use string*/

using System;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Please enter your credit card number:");

        string crdnum = Console.ReadLine(); //takes in reqiured data

        int sum = 0; // generates sum to be used later

        string newNumber = ""; //sets string variable for the new card number after it has been adjusted

        string digit = ""; // sets variable to take in each digit of the card number individually

        int p; // sets position of the string variable

        for (p = 0; p < crdnum.Length; p++) //sets loop for when the positon is less than the card length

        {

            digit = crdnum.Substring(p, 1); // breaks up the card number by every digit

            if (p % 2 != 0) // if the position is an even number  it will convert the digit to an integer and multiply it by 2 and add it to the new number

                newNumber += (Convert.ToInt32(digit) * 2);

            else //if the position is odd or 0 it will add the digit to the new number

            {

                newNumber += digit;

            }

        }

​

        for (p = 0; p < newNumber.Length; p++) //sets position back at 0 and creats a loop for when the position is less than the length of the new number

        {

            sum += Convert.ToInt32(newNumber.Substring(p, 1)); // adds every digit of the new number together to find the sum

        }

​

        if (sum % 10 == 0) // if the sum is divisible by 10 it will be considered valid

            Console.WriteLine("Your card is valid");

        else //if the sum is not divisible by 10 it is considered invalid

            Console.WriteLine("Your card is invalid");

    }

}