03.OperatorsExpressionsStatements/6.FourDigitNumber

//Problem 6.    Four-Digit Number
//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.

using System;

class FourDigitNumber
{
    static void Main()
    {
        Console.Write("Please enter a four-digit number in format abcd:");
        string myString = Console.ReadLine();
        int stringLenght = myString.Length;
        //Check the lenght of string
        if (stringLenght == 4)
        {
            char a = myString[0];
            char b = myString[1];
            char c = myString[2];
            char d = myString[3];

            Console.WriteLine("a={0}", a);
            Console.WriteLine("b={0}", b);
            Console.WriteLine("c={0}", c);
            Console.WriteLine("d={0}", d);

            int firstDigit = Convert.ToInt32(new string(a, 1));
            Console.WriteLine("First digit is {0}.", firstDigit);
            //Check the first digit of the number
            if (firstDigit != 0)
            {
                //Sum of digits
                int sumDigits = (int)Char.GetNumericValue(a) + (int)Char.GetNumericValue(b) +
                    (int)Char.GetNumericValue(c) + (int)Char.GetNumericValue(d);
                Console.WriteLine("The Sum of the digits:{0}", sumDigits);

                //Reverse number
                int newLenghtString = stringLenght - 1;
                Console.Write("The reverse number in format dcba:");
                while (newLenghtString >= 0)
                {
                    string reverseString = "" + myString[newLenghtString];
                    newLenghtString--;
                    Console.Write("{0}", reverseString);
                }
                Console.WriteLine();
                //String in order dabc
                string lastToFirst = d.ToString() + a.ToString() + b.ToString() + c.ToString();
                Console.WriteLine("The number in format dabc:{0}", lastToFirst);
                //String in order acbd
                string secondToThird = a.ToString() + c.ToString() + b.ToString() + d.ToString();
                Console.WriteLine("The number in format acbd:{0}", secondToThird);
            }
            else
            {
                Console.WriteLine("The number cannot start with 0. Please, enter again 4 digits number.");
            }
        }
        else
        {
            Console.WriteLine("The number must be exactly 4 digits. Please, enter again 4 digits number.");
        }
    }
}