using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ConsoleApplication1{    class Program    {        static void Main(string[] args)        {            string str = "天工问答，是天工网旗下专业的免费知识问答平台，帮助建设行业从业者解决在学习和工作中遇到的实际问题，让建筑人不再有疑问";            Dictionary<char, int> dic = new Dictionary<char, int>();            for (int i = 0; i < str.Length; i++)            {                if (!dic.ContainsKey(str[i]))                {                    dic[str[i]] = 1;                }                else                {                    dic[str[i]]++;                }                            }            int maxvalue =http://www.mamicode.com/ dic.Values.Max();            foreach (char c in dic.Keys)            {                if(dic[c]==maxvalue)                {                    Console.WriteLine(c);                    Console.ReadKey();            }            }                    }    }}