public string Save(Student student)
 {
     if (aStudentGateway.IsCourseExists(student))
     {
         return("This course already enrolled");
     }
     else
     {
         int isRowAffected = aStudentGateway.Save(student);
         if (isRowAffected > 0)
         {
             return("Course enrolled successfull");
         }
         else
         {
             return("course enrolled failed");
         }
     }
 }