FourDigits

using System;

class FourDigitNumber
{
    static void Main(string[] args)
    {
        Console.WriteLine("Please enter \"abcd\" - Four-Digit Number");
        int number = int.Parse(Console.ReadLine());

        bool hasFourDigits = (number.ToString().Length == 4);
        while (!hasFourDigits)
        {
            Console.WriteLine("Please write a four-digit number:");
            number = int.Parse(Console.ReadLine());
            hasFourDigits = (number.ToString().Length == 4);
        }

        int a = (number / 1000) % 10;
        int b = (number / 100) % 10;
        int c = (number / 10) % 10;
        int d = number % 10;
        Console.Write("The sum of the digits of the number you have just entered is : ");
        Console.WriteLine(a + b + c + d);
        Console.WriteLine("Print on the console the number in reversed order: {0}{1}{2}{3}", d, c, b, a);
        Console.WriteLine("Puts the last digit in the first position: {0}{1}{2}{3}", d, a, b, c);
        Console.WriteLine("Exchanges the second and the third digits: {0}{1}{2}{3}", a, c, b, d);
    }
}