php - How to add underscore before index? -

i want insert underscore before counting index every time upload multiple files.

what expect:

schools.jpg

schools_1.jpg

schools_2.jpg

schools_3.jpg

my program output:

schools.jpg

schools1.jpg

schools2.jpg

schools3.jpg

here's code:

controller

public function do_upload() {     $this->load->library('upload');     $files = $_files;     $cpt = count($_files['userfile']['name']);      for($i=0; $i<$cpt; $i++) {         $_files['userfile']['name']= $files['userfile']['name'][$i];         $_files['userfile']['type']= $files['userfile']['type'][$i];         $_files['userfile']['tmp_name']= $files['userfile']['tmp_name'][$i];         $_files['userfile']['error']= $files['userfile']['error'][$i];         $_files['userfile']['size']= $files['userfile']['size'][$i];          $this->upload->initialize($this->set_upload_options());         $this->db->insert('tbl_image', $file_array);     } }  private function set_upload_options() {    $config = array(         'image_library' => 'gd2',         'file_name'     => $this->input->post('file_name'),         'upload_path'   => './public/img/uploads',         'upload_url'    => base_url().'public/img/uploads',         'allowed_types' => 'jpg|jpeg|pdf',         'max_size'      => '1024kb',         'max_width'     => '1024',         'max_height'    => '768',         'maintain_ratio'=> true,         'overwrite'     => false,     );     return $config; } 

html

<label for="file">select file upload:</label> <input type="file"  name="userfile[]" multiple/> <label for="file_name">set image file name:</label> <input type="text" size="20" name="file_name" required id="file_name"/> <input type="submit" id="btnsubmit" value="upload file"/> 

i saw lot of wrong suggested answer, put underscore in index of array, this

  $_files['userfile']['name']= $files['userfile']['name'][$i]."_".[$i];   //you can't because $file['userfile']['name'][$i] array better code   $flag=0;             for($i=0; $i<$cpt; $i++) {                 $flag++;                 $_files['userfile']['name']=$files['userfile']['name'][$i];                 $_files['userfile']['type']= $files['userfile']['type'][$i];                 $_files['userfile']['tmp_name']= $files['userfile']['tmp_name'][$i];                 $_files['userfile']['error']= $files['userfile']['error'][$i];                 $_files['userfile']['size']= $files['userfile']['size'][$i];                  $this->upload->initialize($this->set_upload_options($i, $flag));                 $this->db->insert('tbl_image', $file_array);           }   private function set_upload_options($i, $f) {     $charac= "";     if($f>1) {                     $charac=$this->input->post('file_name')."_".$i;           //here code add underscore image 2 , above     }     else {         $charac=$this->input->post('file_name');     }    $config = array(         'image_library' => 'gd2',         'file_name'     => $charac,         'upload_path'   => './public/img/uploads',         'upload_url'    => base_url().'public/img/uploads',         'allowed_types' => 'gif|jpg|jpeg',         'max_size'      => '1024kb',         'max_width'     => '1024',         'max_height'    => '768',         'maintain_ratio'=> true,         'overwrite'     => false,     );     return $config; }