C# 嵌套类

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

namespace ConsoleApplication32
{
class Program
{
public class A
{
public int a { get; set; }
}

}
class IN
{
static void Main(string[] args)
{
Program.A aa = new Program.A();//注意
aa.a = 1;
}
}
}