/*
 * C# Program to Get a Number and Display the Sum of the Digits
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Program
{
class Program
{
    static void Main(string[] args)
    {
        int num, sum = 0, r;
        Console.WriteLine("Enter a Number : ");
        num = int.Parse(Console.ReadLine());
        while (num != 0)
            {
                r = num % 10;
                num = num / 10;
                sum = sum + r;
            }
        Console.WriteLine("Sum of Digits of the Number : "+sum);
        Console.ReadLine();
    }
}
}

Enter a Number : 123
Sum of Digits of the Number : 6