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

namespace Null值相加
{
    class Program
    {
        static void Main(string[] args)
        {
            string str1 = null;
            string str2 = null;

            string str3 = str1 + str2;

            Console.WriteLine("==>两个为null的字符串相加的结果：\n==>" +
                (str3 == null ? "null" : (str3.ToString() == string.Empty ? "string.Empty --> 居然为长度为0的字符串。" : str3.ToString()))
                + System.Environment.NewLine);
            Console.WriteLine("==>相加后字符串[str3]的长度为：" + str3.Length + System.Environment.NewLine);

            Console.WriteLine("==>我操，这是什么原因??????\n\n==>按任意键继续......\n\n=====================\n");

            int? a = null;
            int? b = null;
            int? c = a + b;

            Console.WriteLine("==>两个可空的[int]类型相加的结果：\n" + (c == null ? "==>两个可空的[int]相加结果为null" : "没猜出来是什么结果") + System.Environment.NewLine);

            Console.WriteLine("==>我操，这又是什么原因??????\n\n==>按任意键退出......\n\n");
            Console.ReadKey();
        }
    }
}

  int? a = null;
  int? b = null;
  int? c = a + b;