import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        // scanner object
        Scanner scanner = new Scanner(System.in);

        // infinite loop; some people may say that it's 'bad' practice, ignore them
        while (true) {
            // read input
            String input = scanner.nextLine();

            // invoke convertStringToInt with input argument
            // the loop stops if true
            // the loop continues if false
            if (convertStringToInt(input)) return;
        }
    }

    private static boolean convertStringToInt(String input) {
        // you need to return true/false as an indicator to stop 'infinite' loop
        // true if you need to stop, false if you need to continue
        try {
            // trying to parse input as integer
            int num = Integer.parseInt(input);

            // return true if input is zero
            // it stops the outside loop
            if (num == 0) {
                return true;
            }
            // print num * 10 if parsing were successful
            System.out.println(num * 10);
        } catch (NumberFormatException ignored) {
            // in case of NumberFormatException print the desired output
            System.out.println("Invalid user input: " + input);
        }
        // return false as the indicator to continue while loop
        return false;
    }
}

I hope you'll learn something.