//controller
public function password_check($str)
		{
		   if (!preg_match('#[0-9]#', $str) && preg_match('#[a-zA-Z]#', $str)) {
		     return FALSE;
		   }
		   return TRUE;
		}

	public function str_check($str)
		{
		   if (!preg_match("/^[a-zA-Z ]*$/",$str)) {
		     return FALSE;
		   }
		   return TRUE;
		}
	function loginAction(){
		$username = $this->input->post('username');
		$password = $this->input->post('password');

		$this->form_validation->set_rules('username', 'Username', 'trim|alpha_dash|required|min_length[5]|max_length[18]',
        		array(
		                'min_length'      => '%s anda kurang dari 5 karakter',
		                'alpha_dash' => '%s anda mengandung karakter yang tidak diizinkan'
		        )
		);
		$this->form_validation->set_rules('password', 'Password', 'required|min_length[8]|max_length[20]|callback_password_check',
				array(
					'min_length' => '%s anda kurang dari 8 karakter',
					'password_check' => '%s anda harus mengandung huruf dan angka',
					'max_length' => '%s maximal berjumlah 20 karakter'
				)
		);

		if ($this->form_validation->run() == FALSE)
                {
		$this->load->view('login');
                }
                else
                {
		$where = array(
			'username' => $username,
			'password' => md5($password)
		);

		$cek = $this->m_login->cek_login("user_pb",$where)->num_rows();
		if($cek > 0){
			$data_session = array(
				'nama' => $username,
				'status' => "login"
				);

			$this->session->set_userdata($data_session);

			redirect(base_url("admin/admin_page"));
		}else{
			print "<script type=\"text/javascript\">alert('Username atau password salah!');</script>";
			$this->load->view('login');
		}
		}
	}

//models
function cek_login($table,$where){
		return $this->db->get_where($table,$where);
	}

//views
<form method="post" action="<?php echo base_url('admin/loginAction'); ?>">
                            <fieldset>
                                <div class="form-group">
                                    <!--input class="form-control" placeholder="Username" name="email" type="email" autofocus-->
							<h6 style="font-size: 10px; margin-top: 10px; margin-bottom: 2px"><?php echo form_error('username'); ?></h6>
							<input type="text" name="username" maxlength="20" minlength="6" value="<?php echo set_value('username'); ?>" placeholder="username" class="form-control" required>
                                </div>
                                <div class="form-group">
                                    <!--input class="form-control" placeholder="Password" name="password" type="password" value=""-->
							<h6 style="font-size: 10px; margin-top: 10px; margin-bottom: 2px"><?php echo form_error('password'); ?></h6>
							<input type="password" name="password" value="<?php echo set_value('password'); ?>" minlength="8" maxlength="36" placeholder="password" class="form-control" required>
                                </div>
                                <div class="checkbox">
                                    <label>
                                        <input name="remember" type="checkbox" value="Remember Me">Remember Me
                                    </label>
                                </div>
                                <!-- Change this to a button or input when using this as a form -->
								<button type="submit" style="font-family:baloo bhaijaan" value="login" class="btn btn-lg btn-success btn-block">Masuk</button>
                        </form>