Checked box is correct or not?

I have PHP form. This foreach is execute multiple checkedboxs. I want know, User selected checked boxs C_ID INSERT to the database. This code not working properly.

    <?php
 if(isset($_POST['send'])){
      foreach($_POST['mod'] as $checkbox){
        $checkbox = $values[COURSE_ID];
        echo $checkbox . ' ';

        $date = date("Y-m-d"); 
        $sql= "INSERT INTO REG ( C_ID, REGISTERED, DATE) "
        . "VALUES ('".$values[C_ID]."', 'Y' ,'".$date. "')";
        DBQuery($sql);  
      } 
 }

echo "<form name=send method=post >";
   foreach($result1 as $value) {
    $checked = in_array($value, $selected) ? 'checked="checked"' : '';
    echo '<input type="checkbox" name="mod[]" value="' . $value[C_ID] .'"  ' . $checked . '>'. $value[TITLE] .'</input><br>';
   }
   echo "<button type=submit id=send name=send>send</button>";
   echo "</form>";
   ?>