using System;

public class Program

{

    public static void Main()

    {

var s4 = 

new String(

new char[]{'w', 'o', 'r', 'l', 'd'});

//  s4[1] = 'd'; error - string.this[int] is read only

//https://unicode-table.com/

Console.WriteLine("\u2642 \U0001F47D \x2640");

long number1 = 19876543210;

Console.WriteLine(

number1.ToString("+# (###) ###-##-##"));

Console.WriteLine(

$"{number1:C}"); 

Console.WriteLine(

string.Format("number1={0:X}",19876543210));    

    }

}