string Example = "abcdefff";

                string begin_str = "e";
                string result = Regex.Match(Example, begin_str + @".*?$").Value;//efff

------解决方案--------------------
contains判断,indexof位置
substring截取

------解决方案--------------------
string str1 = "asdcd";
string str2 = str1.Remove(0, str1.IndexOf('s'));

------解决方案--------------------
C# code
string str = "abcdeaksdaslkd";
            str = str.Substring(str.IndexOf('d'), str.Length - str.IndexOf('d'));

------解决方案--------------------
C# code

static void Main(string[] args)
        {
            string str = "485269";
            char c = '8';
            Console.WriteLine(str.Substring(str.IndexOf(c)));
            Console.ReadLine();
        }