<form method="post" action="" name="sentMessage" id="contactForm" novalidate >
                                    <div class="row">
                                        <div class="col-sm-12">
                                            <h3>Registration Form</h3>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <input class="text required" type="text" placeholder="UserName" name="username" id="uname" data-validation-required-message="Please enter your UserName." />
                                                <p class="help-block text-danger"></p>
                                            </div>
                                            <div class="form-group">
                                                <input class="text required" type="text" placeholder="First Name" name="fname" id="fname" data-validation-required-message="Please enter your First Name."/>
                                                <p class="help-block text-danger"></p>
                                            </div>
                                            <div class="form-group">
                                                <input class="text required " type="text" placeholder="Last Name" name="lname" id="lname" data-validation-required-message="Please enter your Last Name."/>
                                                <p class="help-block text-danger"></p>
                                            </div>
                                            <div class="form-group">
                                                <input class="text required email" type="email" placeholder="Email" name="email" id="uemail" data-validation-required-message="Please enter your Email."/>
                                                <p class="help-block text-danger"></p>
                                            </div>
                                            <div class="form-group">
                                                <input class="text required" type="password" placeholder="Password" name="password" id="upassword" data-validation-required-message="Please enter your Password."/>
                                                <p class="help-block text-danger"></p>
                                            </div>
                                            <div class="form-group">
                                                <input class="text required" type="password" placeholder="Confirm Password" name="cpassword" id="cpassword" data-validation-required-message="Please enter your Password."/>
                                                <p class="help-block text-danger"></p>
                                            </div>
                                        </div>
                                    </div>
                                    <div class="row">
                                        <div class="col-xs-12 rst-contactsubmit">
                                            <div class="form-group">
                                                 <!-- required data-validation-required-message="Please enter your message." -->
                                                <p class="help-block text-danger"></p>
                                                <div id="success"></div>
                                            </div>
                                            <input class="btn btn-primary btn-lg" type="submit" value="REGISTER" />
                                        </div>
                                    </div>
                                </form>

if( jQuery("#contactForm").length ) {
        jQuery("#contactForm input").jqBootstrapValidation({
            preventSubmit: true,
            submitError: function(jQueryform, event, errors) {
                // additional error messages or events
            },
            submitSuccess: function(jQueryform, event) {
                event.preventDefault(); // prevent default submit behaviour
                // get values from FORM
                var username = jQuery("input#contact-username").val();
                var fname = jQuery("input#contact-fname").val();
                var lname = jQuery("input#contact-lname").val();
                var email = jQuery("input#contact-email").val();
                var password = jQuery("input#contact-password").val();
                var firstName = fname; // For Success/Failure Message
                // Check for white space in name for Success/Fail message
                if (firstName.indexOf(' ') >= 0) {
                    firstName = fname.split(' ').slice(0, -1).join(' ');
                }
                jQuery.ajax({
                    type: "POST",
                    url: "<?php echo base_url()?>index.php/login/create_user",
                    data: {
                        username: username,
                        fname: fname,
                        lname: lname,
                        email: email,
                        password: password,
                    },
                    cache: false,
                    success: function() {
                        // Success message
                        jQuery('#success').html("<div class='alert alert-success'>");
                        jQuery('#success > .alert-success').html("<button type='button' class='close' data-dismiss='alert' aria-hidden='true'>&times;")
                            .append("</button>");
                        jQuery('#success > .alert-success')
                            .append("<strong>Your message has been sent. </strong>");
                        jQuery('#success > .alert-success')
                            .append('</div>');

                        //clear all fields
                        jQuery('#contactForm').trigger("reset");
                    },
                    error: function() {
                        // Fail message
                        jQuery('#success').html("<div class='alert alert-danger'>");
                        jQuery('#success > .alert-danger').html("<button type='button' class='close' data-dismiss='alert' aria-hidden='true'>&times;")
                            .append("</button>");
                        jQuery('#success > .alert-danger').append("<strong>Sorry " + firstName + ", it seems that server is not responding. Please try again later!");
                        jQuery('#success > .alert-danger').append('</div>');
                        //clear all fields
                        jQuery('#contactForm').trigger("reset");
                    },
                })
            },
            filter: function() {
                return jQuery(this).is(":visible");
            }
        });
    }

<?php

function __construct()
{
    parent::__construct();
}

public function index(){

    $this->load->helper(array('form'));
    $this->load->view('login');

}

function validate_credentials(){

    $this->load->model('membership_model');
    $query = $this->membership_model->validate();

    if($query){

        $data = array('username' => $this->input->post('username'), 'is_logged_in' => true);
        $this->session->set_userdata($data);
        redirect('<?php base_url()index.php/user_dashboard');
    }
}

function create_user(){

    $this->load->library('form_validation');
    $this->form_validation->set_rules('username', 'Username', 'trim|required|callback_check_username');
    $this->form_validation->set_rules('fname', 'Name', 'trim|required');
    $this->form_validation->set_rules('lname', 'Last Name', 'trim|required');
    $this->form_validation->set_rules('email', 'Email-id', 'trim|required|valid_email|callback_check_email');
    $this->form_validation->set_rules('password', 'Password', 'trim|required|min_length[4]');
    $this->form_validation->set_rules('cpassword', 'Confirm Password', 'trim|required|matches[password]');

    if($this->form_validation->run() == FALSE){
        echo "fail";
    }

    else{
        $this->load->model('membership_model');

        if($query = $this->membership_model->create_user())
        {
            $data['account created'] = 'your account is created';
            $this->load->view('login', $data);
        }
        else{
            $this->load->view('register');
        }
    }

}

function check_username($requested_username){
    $this->load->model('membership_model');

    $username_available = $this->membership_model->check_username($requested_username);

    if($username_available){
        return TRUE;
    }
    else{
        return FALSE;
    }
}

function check_email($requested_email){

    $this->load->model('membership_model');

    $email_available = $this->membership_model->check_email($requested_email);

    if($email_available){
        return TRUE;
    }
    else{
        return FLASE;
    }
}