// Version at the end of class -
// Almost but not quite the solution!! See the handout

// Determine the last digit of a credit card number
//
// 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)

public class Credit {
	public static void main(String[] args) {
		String credit = "123456789";
		int sum = 0;
		for (int i=credit.length()-1; i>=0; i=i-2) {
			char c = credit.charAt(i);
			int num = 2*Character.getNumericValue(c);
			sum = sum + num/10 + num%10;
			System.out.println("sum:" + sum + ", num:" + num);
		}
		for (int i=credit.length()-2; i>=0; i=i-2) {
			char c = credit.charAt(i);
			int num = Character.getNumericValue(c);
			sum = sum + num/10 + num%10;
			System.out.println("sum:" + sum + ", num:" + num);
		}
		System.out.println("last digit should be:" + (10-sum%10));
	}
}