Declare a variable of type int. Prompt the user for a positive three-digit number. Test to ensure the number is within the proper bounds. If the number is larger or less than three digits, output "Error" and terminate the program. Otherwise, calculate and print the sum of the three digits.

// Scanner class is imported to allow program

// receive input

import java.util.Scanner;

// Solution class is defined

public class Solution {

   // main method that signify beginning of program execution

   public static void main(String args[]) {

       // Scanner object scan is created

       // it receive input via keyboard

       Scanner scan = new Scanner(System.in);

       // Prompt is display asking the user to enter number

       System.out.println("Enter your three digit number: ");

       // the user input is stored at userInput

       int userInput = scan.nextInt();

       // if-statement that check if user input is three digit

       if(userInput < 100 || userInput > 999){

           // if input is three digit; it display error

           System.out.println("Error");

       } else{

           // the first digit is gotten as the quotient

           // when the input is divided by 100

           int firstDigit = userInput / 100;

           // the second digit is gotten by dividing the

           // result of the input modulus 100 by 10

           int secondDigit = (userInput % 100) / 10;

           // the third digit is gotten through

           // userInput modulus 10

           int thirdDigit = userInput % 10;

           // the addition of the three digit is assigned to sum

           int sum = firstDigit + secondDigit + thirdDigit;

           // the sum is displayed to the user

           System.out.println("The sum of the three digit is: " + sum);

       }

   }

}

Explanation:

The program is well commented and detailed. Images showing output of the program is attached.

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hope this is what you're talking about