//PUT Methods
 public string UpdateBook(Students student, string NIM)
 {
     bool updated = repository.UpdateAStudents(student);
     if (updated)
         return "Student with id = " + NIM + " updated successfully";
     else
         return "Unable to update student with NIM = " + NIM;
 }
 //1. Create Students
 public Students AddNewStudents(Students newStudent)
 {
     if (newStudent == null)
         throw new ArgumentNullException("newStudent");
     newStudent.NIM = counter++;
     students.Add(newStudent);
     return newStudent;
 }
 //3. Update Students
 public bool UpdateAStudents(Students updatedStudents)
 {
     if (updatedStudents == null)
         throw new ArgumentNullException("updatedStudent");
     int idx = students.FindIndex(b => b.NIM == updatedStudents.NIM);
     if (idx == -1)
         return false;
     students.RemoveAt(idx);
     students.Add(updatedStudents);
     return true;
 }
 //POST Methods
 public string AddBook(Students student, string NIM)
 {
     Students newStudent = repository.AddNewStudents(student);
     return "NIM =" + newStudent.NIM;
 }