using System;

​

public class SumOfDigits

{

    public static int CalculateSumOfDigits(string input)

    {

        // Input validation: Check if the input is null or empty.

        if (string.IsNullOrEmpty(input))

        {

            throw new ArgumentException("Input cannot be null or empty.");

        }

​

        // Input validation: Check if the input is a valid positive integer.

        if (!int.TryParse(input, out int number))

        {

            throw new ArgumentException("Input must be a valid integer.");

        }

​

        // Input validation: Check if the number is positive.

        if (number <= 0)

        {

            throw new ArgumentException("Input must be a positive integer.");

        }

​

        int sum = 0;

        string numberStr = number.ToString(); // Convert the number to string for easier digit access.

​

        // Iterate through the digits of the number and add them to the sum.

        for (int i = 0; i < numberStr.Length; i++)

        {

            // Subtract '0' to convert the character digit to its integer value.

            sum += numberStr[i] - '0';

        }

​

        return sum;

    }

​

    public static void Main(string[] args)

    {

        Console.WriteLine("Enter a positive integer: ");

        string input = Console.ReadLine();

​

        try

        {

            int sum = CalculateSumOfDigits(input);

            Console.WriteLine("The sum of digits of a given positive integer is " + sum);

        }

        catch (ArgumentException ex)

        {

            Console.WriteLine(ex.Message);

        }

        catch (Exception ex)

        {

            Console.WriteLine("An error occurred: " + ex.Message);

        }

    }

}