C#---字典按值升序，判断键是否存在，遍历

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace lianxi1{    class Program    {        static void Main(string[] args)        {            Dictionary<int, int> d = new Dictionary<int, int>();            d[1] = 1;            d[2] = 2;            var keyvalues = from keyvalue in d orderby keyvalue.Value ascending select keyvalue;            foreach (var keyvalue in keyvalues)                if (!d.ContainsKey(3))                    d[3] = 3;            foreach (var keyvalue in keyvalues)                Console.WriteLine(keyvalue.Value);            Console.ReadKey();        }    }}