测试下

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _04我的字符串
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] strs = new string[] { "xiaoming", "laowang", "xiaowang" };
            MyString ms = new MyString();
            ms.ChangeString(strs, StringToUpper);
            foreach (string item in strs)
            {
                Console.WriteLine(item);
            }

            Console.ReadKey();
        }

        public static string Add(string str)
        {
            return "=" + str + "=";
        }

        public static string StringToUpper(string str)
        {
            return str.ToUpper();
        }
    }
}