using System;

public class Program

{

    public static void Main()

    {

        Console.Write("Nhap vao mot chuoi: ");

            string ch = Console.ReadLine();

            Console.WriteLine("In hoa: {0}", ChuyenDoi(ch));

            Console.ReadLine();

        }

        static string ChuyenDoi(string chuoi)

        {

            string str = "";

            foreach (char item in chuoi)

            {

                if (item >= 'a' && item <= 'z')

                    str += Convert.ToChar((int)item - 32).ToString();

                else

                    str += item.ToString();

            }

            return str;

        }

    }

​