private void AddCourse(object obj) { if (CourseName == null || CourseName.Length == 0) { Output = "Please enter course name"; return; } if (CourseID == null || CourseID.Length == 0) { Output = "Please enter course ID"; return; } foreach (char c in CourseID.Trim()) { if (c < '0' || c > '9') { Output = "courseID can only contain numbers, invalid character '" + c + "'"; return; } } if (MaxPart == null || MaxPart.Length == 0) { Output = "Please enter max number of participants"; return; } try { Dal.AddCourse(CourseID, CourseName, int.Parse(MaxPart)); Output = "Course added"; } catch (Exception e) { HandleException(e); } }