codeigniter中的模型将无法识别ID号

So here is the error:

A PHP Error was encountered

Severity: Notice

Message: Undefined variable: idnum

Filename: models/model_teacher.php

Line Number: 8

this is my controller:

 public function teacher(){

   $this->load->model('model_teacher');

   $data['result'] = $this->model_teacher->scoreboard();
   $this->load->view('teacher/teacher', $data);
  }

and my model:

 class Model_teacher extends CI_Model {

    public function scoreboard() {

        $this->db->where('login_id', $this->input->post('idnum'));
        $query = $this->db->query("SELECT * FROM teacher WHERE login_id = '".$idnum."'");
        return $query->result();

        }
} 

and the view:

<?php
  foreach ($result as $row) {
            echo $row->login_id."<br>";
            echo $row->lname."<br>";
        }
?>

and don't know what is wrong with this code. please bear with me, i'm still a newbie at using codeigniter. thanks guys.

you can't get directly in model you have to first get in controller Controller

   public function teacher(){
$id  = $this->input->post('idnum');

   $this->load->model('model_teacher');

   $data['result'] = $this->model_teacher->scoreboard($id);
   $this->load->view('teacher/teacher', $data);
  }

Model`

public function scoreboard($idnum) {

    $query = $this->db->query("SELECT * FROM teacher WHERE login_id = '".$idnum."'");
    return $query->result();

    }`

This is the code you can use

Change as following:

In Controller

 public function teacher(){
   $this->load->model('model_teacher');
   $idNum = $this->input->post('idnum');
   $data['result'] = $this->model_teacher->scoreboard($idNum);
   $this->load->view('teacher/teacher', $data);
  }

In Model

   public function scoreboard($idNum) {
      $this->db->where('login_id', $idNum);
      $query = $this->db->query("SELECT * FROM teacher WHERE login_id = '".$idnum."'");
      return $query->result();
   }

Would be better if you pass it from controller to model

$id = $this->input->post('idnum');
$data['result'] = $this->model_teacher->scoreboard($id);

and model:-

public function scoreboard($id) {
  //$this->db->where('login_id', $id);
  $query = $this->db->query("SELECT * FROM teacher WHERE login_id = '".$id."'");
  return $query->result();
}

Also you haven't define anywhere $idnum so notices comes up