ISBN

/**
 * This program inputs a number and checks whether the number entered is a valid ISBN or not.
 */
import java.util.Scanner;
public class ISBN
{
    static int getSum(long num) //Function to get the required sum of all the digits.
    {
        int i, x, sum = 0;
        String a = Long.toString(num);
        for(i=0;i<a.length();i++)
        {
            x = Character.getNumericValue(a.charAt(i));
            sum += (i+1) * x;
        }

        return sum;
    }

    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        //Getting the ISBN.
        System.out.println("Please enter a 10-digit ISBN.");
        long num = sc.nextLong();
        //Checking the length.
        String a = Long.toString(num);
        if(a.length() == 10)
        {
        int sum = getSum(num);
        if(sum % 11 == 0)
            System.out.println("The number entered is a valid ISBN!");
        else
            System.out.println("The number entered is not a valid ISBN.");
        }
        else
            System.out.println("The number entered is not a valid ISBN. It must be exactly 10 digits long.");

        sc.close();
    }
}