字符串中的字符串不是空的，但没有显示任何内容..可能出错？

So I have this switch case condition here ... it gets recognized by PHP, but when I do the var_dump($input) at the end , it returns string(172) "" , but not the actual fields .. What's going wrong ? var_dump($value['element_type']) returns "simple_name"

var_dump($value['element_type']); 

switch ($value['element_type']) {
  case "simple_name":
    $input .= "<tr>"; 
    $input .= "<td>First Name</td>"; 
    $input .= "<td><input type=\"text\" name=\"{$name}_first\" value=\"" . stripslashes($_POST["{$name}_first"]) . "\" /></td>";
    $input .= "</tr>";
    $input .= " <tr>";
    $input .= "<td>Last Name</td>";
    $input .= "<td><input type=\"text\" name=\"{$name}_last\" value=\"" . stripslashes($_POST["{$name}_last"]) . "\" /></td>";
    $input .= " </tr>"; var_dump($input);exit;

    if (isset($form_errors["{$name}_first"]) && isset($form_errors["{$name}_last"]))
      $error_string = "$label is required";
    else
      $error_string = $form_errors["{$name}_first"] . $form_errors["{$name}_last"];
      $value['element_layout'] = " ";
    break;