Product of Digits

/*
 * Problem : Multiply all digits of a number.
 * Input   : One integer.
 * Output  : The product of the digits.
 * Approach: Take digits one by one and multiply.
 * Time    : O(d)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        long number = Math.abs(new Scanner(System.in).nextLong());

        // Step 1: Handle 0 first. Its only digit is 0, so the product is 0.
        if (number == 0) {
            System.out.println(0);
            return;
        }

        // Step 2: Start the product with 1, because 1 does not change a product.
        long product = 1;

        // Step 3: Repeat until no digits are left.
        while (number > 0) {
            // Step 4: Take the last digit and multiply it into the product. Example: 123 % 10 = 3.
            product = product * (number % 10);

            // Step 5: Remove the last digit. Example: 123 / 10 = 12.
            number = number / 10;
        }

        // Step 6: Print the product.
        System.out.println(product);
    }
}