using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("----------------------------------");

        Console.WriteLine("TEST\n----------------------------------");

        Test("abcdef");

        Test("pqksuvy");

        Test("zyxwvutsrqponmlkjihgfedcba");

        Console.WriteLine("\n----------------------------------");

        Console.WriteLine("User\n----------------------------------");

        string input = getInput();

        Test(input);

    }

    // Turns string to array of chars then sort

    static string output(string input)

    {

        char[] userInput = input.ToCharArray();

        Array.Sort(userInput);

        string output = new string(userInput);

        return output;

    }

    static string getInput()

    {

        string input;

        bool validInput = false;

        do

        {

            Console.WriteLine("Enter up to 26 letters: ");

            input = Console.ReadLine();

            if (input.Length <= 26)

                validInput = isOnlyLetters(input);

        } while (!validInput);

​

        return input;

    }

    static bool isOnlyLetters(string s)

    {

        foreach (char c in s)

        {

            if (!Char.IsLetter(c))

            {

                return false;

            }

        }

        return true;

    }

    static void Test(string input)

    {

        Console.WriteLine("Input: " + input);

        Console.WriteLine("Output: " + output(input));

    }

}