using System;

public class Program

{

    public static void Main()

    {

            //  Write a program that takes as input a four-digit number in format abcd (e.g. 2011) and performs the following:

            //• Calculates the sum of the digits (in our example 2+0+1+1 = 4).

            //• Prints on the console the number in reversed order: dcba (in our example 1102).

            //• Puts the last digit in the first position: dabc (in our example 1201).

            //• Exchanges the second and the third digits: acbd (in our example 2101).

            //The number has always exactly 4 digits and cannot start with 0. 

​

            Console.Write("Please enter the same number: ");

            int number;

            while (!int.TryParse(Console.ReadLine(), out number) || number < 1000 || number > 9999) Console.WriteLine("Invalid number!!!");

​

            string strNumber = Convert.ToString(number);

​

            SumOfDigits(strNumber);

​

            ReversedDigit(strNumber);

​

            string exchangedLasWithFirst = strNumber[3] + "" + strNumber[0] + strNumber[1] + strNumber[2];

            Console.WriteLine("Last digit in front: {0}", exchangedLasWithFirst);

​

            string exchangedSecondWithThird = strNumber[0] + "" + strNumber[2] + strNumber[1] + strNumber[3];

            Console.WriteLine("Exchanged second with third: {0}", exchangedSecondWithThird);

​

        }

​

        private static void ReversedDigit(string strNumber)

        {

            int result = 0;

​

            for (int i = strNumber.Length - 1; i >= 0; i--)

            {

                if (i == strNumber.Length - 1)

                {

                    result += strNumber[i] - 48;

                }

                else

                {

                    result = (result*10) + ((strNumber[i] - 48));

                }

            }

​

            Console.WriteLine("Reversed digit is: {0}", result);

        }

​

        private static void SumOfDigits(string strNumber)

        {

            int result = 0;

​

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

            {

                result += strNumber[i] - 48;

            }

​

            Console.WriteLine("The sum of digits is: {0}", result);

        }

}