public string Save(CourseAssign courseAssign)
        {
            if (courseAssignGateway.IsSubjectExsists(courseAssign))
            {
                return("The Course is already Assigned");
            }
            else
            {
                float Credit          = Convert.ToSingle(courseAssignGateway.GetCourseId(courseAssign.CourseCode).Credit);
                float AvailableCredit = Convert.ToSingle(courseAssignGateway.GetAvailableCreditByTeacherId(courseAssign.TeacherId).ReminingCredit);
                float RemainingCredit = (AvailableCredit - Credit);


                int rowAffect = courseAssignGateway.UpdateTeacher(courseAssign.TeacherId, RemainingCredit);
                if (rowAffect > 0)
                {
                    int affect = courseAssignGateway.Save(courseAssign);
                    if (affect > 0)
                    {
                        return("Save Successfully");
                    }
                    else
                    {
                        return("Failed");
                    }
                }

                else
                {
                    return("Failed");
                }
            }
        }