Add table and fieldname

Hi. im going to add database table and field and of course the field type,auto_increment and so on..  and  
may i ask what what is wrong with this?

PHP Code:

$tblname = $this->input->post('tblname');
        $fldname = $this->input->post('fld_name[]');
        
                $fldtype = $this->input->post('fld_type');
                $fldauth = $this->input->post('fld_aut');
                $fldlgth = $this->input->post('fld_lgth');
                
        for($i = 0; $i < count($fldname); $i++)    
            {
                $insert = [[$fldname] => ['type' => $fldtype,
                            'auto_increment' => $fldauth,
                            'constraint' => $fldlgth,
                            'null' =>TRUE]];
                
                $this->dbforge->add_field($insert);
                $this->dbforge->add_key($fldname, TRUE);
                $this->dbforge->create_table($tblname, TRUE);
            } 


Thanks