// Verifying a credit card number
// NOTE: This is not quite the solution to the problem
// of computing the last digit - See the handout
// This must be modified slightly to compute the last digit

// Method for verifying a credit card number:
// 1. Starting with the second digit from the right,
//	  double every other digit
// 2. Break into digits, and add the digits together
// 3. Result must end with 0 (e.g 70)

import java.util.*;

public class Credit1 {
	public static void main(String[] args) {
		Scanner console = new Scanner(System.in);
		System.out.print("Enter credit card number: ");
		String number = console.next();
		System.out.println("Finding last digit for " + number);
		int sum = 0;
		// Add up the digits formed by doubling every other digit
		for (int i=number.length()-2; i>=0; i = i-2) {
			char c = number.charAt(i);
			int n = 2* Character.getNumericValue(c);
			sum = sum + n/10 + n%10;	// Break into two digits and add
			System.out.println("c: " + c + ", n: " + n +
			 	", sum: " + sum);
		}
		// Add the remaining digits
		for (int i=number.length()-1; i>=0; i = i-2) {
			char c = number.charAt(i);
			int n = Character.getNumericValue(c);
			sum = sum + n;
			System.out.println("c: " + c + ", n: " + n +
			 	", sum: " + sum);
		}
	}
}