PHP验证一次显示所有错误

我使用下面的脚本进行验证。我想知道是否有一种方法来转换这个脚本，一次显示所有的错误，而不是一次一个?此外，还有什么我可以做，以防止头部注入?

谢谢。

<?php
session_start();
/* Check all form inputs */
$fname   = check_input($_POST['fname'], "Friend's Name cannot be empty.");
$femail  = check_input($_POST['femail'], "Friend's email cannot be empty.");
$yname   = check_input($_POST['yname'], "Your Name cannot be empty.");
$yemail  = check_input($_POST['yemail'], "Your email cannot be empty.");
$subject  = check_input($_POST['subject'], "Subject cannot be empty.");
$comments  = check_input($_POST['comments'], "Comments cannot be empty.");
/*  alphabet only */
if(!preg_match("/^([A-Za-z's'-]{2,45})$/i", $fname))
{ 
show_error("Friend's name is not valid.");
}
/* If e-mail is not valid show error message */
if (!preg_match("/(['w'-]+'@['w'-]+'.['w'-]+)/", $femail))
{
show_error("Your friend's email address is not valid.");
}
if(!preg_match("/^([A-Za-z's'-]{2,45})$/i", $yname))
{ 
show_error("Your name is not valid.");
}
/* If e-mail is not valid show error message */
if (!preg_match("/(['w'-]+'@['w'-]+'.['w'-]+)/", $yemail))
{
show_error("Your email address is not valid.");
}
htmlentities ($message, ENT_QUOTES);

function check_input($data, $problem='')
{
$data = trim($data);
$data = stripslashes($data);
$data = htmlentities($data);
if ($problem && strlen($data) == 0)
{
    show_error($problem);
}
return $data;
}
function show_error($myError)
{
?>