Problem in single quote

[eluser]Tamilmani[/eluser]
My Controller Code

function addUser()
{
$rules['username']="required";
$rules['password']="required";
$rules['fisrtname']="";
$rules['lastname']="";
$rules['address']=""
$this->validation->set_rules($rules);

$fields['username']="UserName";
$fields['password']="Password";
$fields['fisrtname']="";
$fields['lastname']="";
$fields['address']=""
$this->validation->set_rules($fields);
if($this->valdiation->run()== FALSE)
{

}
else
{
$firstname= addslashes($this->validation->firstname);
$this->User_Model->addnewUser($this->validation->username,$this->validation->password,$firstname,$this->validation->lastname,$this->validation->address);
}
}


Model Code

function addnewUser($username,$password,$firstname,$lastname,$address)
{
$this->db->query("insert into users(UserName,Password,FirstName,LastName,Address)values('$username','$password','$firstname','$lastname','$address')");
return $this->db->insert_id();
}