$this->session->set_flashdata("success","New User Register Successfull..!");
redirect("user","refresh");

$this->session->set_flashdata('error','Rong User Details');
redirect("user","refresh");

<?php
    if ($this->session->flashdata('success')) { ?>
        <div class="alert alert-success">
            <?php echo $this->session->flashdata('success'); ?>
        </div>
    <?php
     ?>
    <?php
    if ($this->session->flashdata('error')) { ?>
        <div class="alert alert-danger">
            <?php echo $this->session->flashdata('error'); ?>
        </div>
    <?php
?>