Controlador

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
/**
 * @author ralf
 * @desc Clase IMC que contiene los calculos aritmeticos
 * **/
class Imc extends CI_Controller{

    public function __construct(){
        parent::__construct();
        $this->load->model('imc_model');
        $this->load->helper(array('url','language'));
    }

    public function index(){
        //https://pastebin.com/xfhPyQ63
        $this->load->helper(array('form', 'url'));
        $this->load->library('form_validation');
        //
        $this->form_validation->set_error_delimiters('<div class="alert alert-danger">', '</div>');
        $this->form_validation->set_rules('peso', 'Peso', 'required|trim|max_length[3]|integer');
        $this->form_validation->set_rules('estatura', 'Estatura', 'required|trim|max_length[3]|integer');
        //
        if ($this->form_validation->run() == FALSE){
            $this->load->view("imc_view");
        }else{
            //TRUE del formulario
            $datos['calculo'] = $this->input->post('peso') / ($this->input->post('estatura') * $this->input->post('estatura'));
            $this->imc_model->insertar($datos);
            $this->load->view("imc_view", $datos);

        }
    }
}