public IActionResult change([FromForm] int id = 0, string Name = null, int IsElective = 0, int Credit = 0)
        {
            bool flag = false;

            this.ViewData["id"] = id;
            if (Name != null)
            {
                flag = courses.Change(id, Name, IsElective, Credit);
            }
            else if (id != 0)
            {
                this.ViewData["oldInf"] = courses.Search(id).FirstOrDefault();
            }
            this.ViewData["flag"] = flag;
            return(View());
        }