Wellcome to ITPG ^^

using System;
using System.Collections.Generic;
using System.Text;
namespace CITB09111
{
    class Program
    {
        static void Main(string[] args)
        {
            string ch1;
            string ch2;
            Console.Write("Nhap chuoi ch1 : ");
            ch1 = Console.ReadLine();
            ch2 = ch1;
            ch2=ch2.ToLower();
            Console.WriteLine(ch2);
            for (int i = 0; i <= (ch1.Length-1); i++)
                Console.Write(ch1[ch1.Length-i-1]);
                Console.ReadLine();
        }
    }
}