$this->load->library('form_validation');

$this->form_validation->set_rules('username','User Name','required|alpha|trim');
$this->form_validation->set_rules('password','Password','required');

$this->form_validation->set_error_delimiters("<p class='text-danger'>","</p>");

echo $username=$this->input->post('username');
echo $password=$this->input->post('password');

if( $this->form_validation->run() )
{
    $this->load->view("success");
}
else
{
    $this->load->view("login");
}

<?php echo form_input(['name'=>'username','class'=>'form-control','placeholder'=>'USERNAME','value'=>set_value('username')]); ?>
<?php echo form_error('username'); ?>
<?php if( $error = $this->session->flashdata('login_failed1')): ?>
     <?= $error ?>
<?php endif; ?>

 <?php echo form_password(['name'=>'password','class'=>'form-control','placeholder'=>'PASSWORD','value'=>set_value('password')]); ?>
<?php echo form_error('password'); ?>
<?php if( $error = $this->session->flashdata('login_failed')): ?>
         <?= $error ?>
<?php endif; ?>