获取某个字符在字符串中出现的次数

  public  static int Count(string WithinString, string search)
        {
            if (string.IsNullOrEmpty(search))
                throw new ArgumentNullException("search");
            int counter = 0;
            int index = WithinString.IndexOf(search, 0);
            while (index >= 0 && index < WithinString.Length)
            {
                counter++;
                index = WithinString.IndexOf(search, index + search.Length);
            }
            return counter;
        }