Erro Undefined index ao realizar login.

Notice: Undefined index: login in C:\Program Files (x86)\EasyPHP-DevServer-13.1VC9\data\localweb\phpteste1\login.php

on line 18

Notice: Undefined index: senhain C:\Program Files (x86)\EasyPHP-DevServer-13.1VC9\data\localweb\phpteste1\login.php

on line 19

form:

<form name="login" method="post" action="login.php">
 <table id="login_table">
 <tr>
 <td>Email:</td>
 <td><input type="text" name="login" id="id_login" class="txt" maxlength="25" /></td>
 </tr>
 <tr>
 <td>Senha:</td>
 <td><input type="password" name="senha" id="id_senha" class="txt" maxlength="20" /></td>
 </tr>
 <tr>
 <td colspan="2"><input type="submit" value="Entrar" class="btn" id="btnEntrar" name="btnEntrar">
  <a href="pagina-do-cliente-cad.php"><input type="button" value="Cadastre-se" class="btn" id="btnCad" name="btnCad"></a></td>
 </tr>
 </table>
 </form>

login.php:

<?php
class Sql{

	public $host, $user, $pass, $query;

	public function __construct(){
 mysql_connect($this -> host = 'localhost', $this -> user = 'root', $this -> pass = '1234' );
 mysql_select_db('cadastro');
	}
	public function query($qr){
 $this -> query = mysql_query($qr);
 return $this -> query;
	}
	public function retornar(){
 return $this -> query;
}
	}
$sql = new sql;
$login = $_POST['login'];
$pwd = $_POST['senha'];
$selecionar = $sql -> query("SELECT * FROM USUARIO WHERE LOGIN = '$login' AND SENHA = '$pwd'");
$c = mysql_num_rows($selecionar);
if($c){
	echo "<meta http-equiv='refresh' content='0, url='pagina-do-cliente-interface.php'>";
	echo 'logado';

	echo "<script>alert('Email ou senha incorretos.'); history.back();</script>";
	echo 'deslogado';
}
?>