//示例： string 的内存模型
namespace ConsoleApplication2
{
  class Program
  {
    static void Main(string[] args)
    {
      string a = "1234";
      string b = a;//a,and b point to the same address
      Console.WriteLine(a);
      Console.WriteLine(b);
 
      a = "5678";
      Console.WriteLine(a);
      Console.WriteLine(b);//That b's value is not changed means string's value cann't be changed

      Console.ReadKey();
    } 
  }
}

//示例： StringBuilder 的内存模型
namespace ConsoleApplication3
{
  class Program
  {
    static void Main(string[] args)
    {
      StringBuilder a = new StringBuilder("1234");
      StringBuilder b = new StringBuilder();
      b = a;
      a.Clear();
      a.Append("5678");
      Console.WriteLine(a);
      Console.WriteLine(b);
      Console.ReadKey();
    }
    
  }
}