//using lambda predicate
 public static IEnumerable<Student> SelectByAgeBetween18_24Labda(Student[] arr)
 {
     var selected = arr.Where(student => student.Age >= 18 && student.Age <= 24);
     return selected;
 }
 //using lambda predicate
 public static IEnumerable<Student> SelectFirstBeforeLastNameLambda(Student[] arr)
 {
     var selected = arr.Where(student => student.FirstName.CompareTo(student.LastName) < 0);
     return selected;
 }