public void Add(students s, courses c)
 {
     this.st = s;
     this.cr = c;
     Console.Write("Enter Avg: ");
     this.avg = Convert.ToInt32(Console.ReadLine());
 }
 public selectCourses(students s, courses c, int av)
 {
     this.st  = s;
     this.cr  = c;
     this.avg = av;
 }