using System;

public class Program

{

    public static void Main()

    {

        var str="hello";

        str=str.ChangeFirstLetterCase();

        var str2="hello2";

        str2=StringHelper.ChangeFirstLetterCase(str2);

        Console.WriteLine(str+""+str2);

    }

}

public static class StringHelper

{

    public static string ChangeFirstLetterCase(this string inputString)

    {

        if (inputString.Length > 0)

        {

            char[] charArray = inputString.ToCharArray();

            charArray[0] = char.IsUpper(charArray[0]) ? 

                char.ToLower(charArray[0]) : char.ToUpper(charArray[0]);

            return new string(charArray);

        }

​

        return inputString;

    }

​

}

​