Styjun

I know how to display an Error message if the user enters a number below 10 or higher than 999 but how can I code to make sure the program doesn't end after the users enter a number below 10 or higher than 999 and give them a second chance to enter their valid input over and over again until they give a correct input.

import java.util.Scanner; 

public class Ex1 

public static void main(String args[]) number>999)
 System.out.println("Error!: "); 
else
 System.out.println("The sum of all digits in " +number + " is " + sum);

You will need to use a loop, which basically, well, loops around your code until a certain condition is met.

A simple way to do this is with a do/while loop. For the example below, I will use what's called an "infinite loop." That is, it will continue to loop forever unless something breaks it up.

import java.util.Scanner;

class Main 
 public static void main(String[] args) 

 Scanner scanner = new Scanner(System.in);

 int num;

 // Start a loop that will continue until the user enters a number between 1 and 10
 while (true) num > 10) 
 System.out.println("Error: Number is not between 1 and 10!n");
 else 
 // Exit the while loop, since we have a valid number
 break;
 
 

 System.out.println("Number entered is " + num);

 

Another method, as suggested by MadProgrammer, is to use a do/while loop. For this example, I've also added some validation to ensure the user enters a valid integer, thus avoiding some Exceptions:

import java.util.Scanner;

class Main 
 public static void main(String[] args) 

 Scanner scanner = new Scanner(System.in);

 int num;

 // Start the loop
 do 

 System.out.println("Please enter a number between 1 - 10:");

 try 
 // Attempt to capture the integer entered by the user. If the entry was not numeric, show
 // an appropriate error message.
 num = Integer.parseInt(scanner.nextLine());
 catch (NumberFormatException e) 
 System.out.println("Error: Please enter only numeric characters!");
 num = -1;

 // Skip the rest of the loop and return to the beginning
 continue;
 

 // We have a valid integer input; let's make sure it's within the range we wanted.
 if (num < 1 while (num < 1 

Try this, i just include the while loop in your code it will work fine.

public static void main(String[] args) 

private static int askInput(Scanner input) 
 int number = input.nextInt();
 return number;