int类型转换舍入问题

一，看代码

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

namespace TestNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            int i1 =  / ;   //2.5
            int i2 =  / ;  //5.5
            int i3 =  / ;    //4.6....
            int i4 = Convert.ToInt32(5.5);
            int i5 = Convert.ToInt32(2.5);
            int i6 = Convert.ToInt32(2.6);
            Console.WriteLine(i1);
            Console.WriteLine(i2);
            Console.WriteLine(i3);
            Console.WriteLine(i4);
            Console.WriteLine(i5);
            Console.WriteLine(i6);
            Console.ReadKey();
        }
    }
}

二，输出