Error messages

[jerrylouise]

how do i add error messages, i want the first one under the box "to" to compare with my database table "users" were the "to" must match a username and if it dosnt it will display the error, and the subject must display a error if there is no subject, same for the body.
And i would also love to know how to get the editng arround a text box like this site has for smilies and font editing.

<table width="100%" border="0" cellpadding="3" cellspacing="0" >
<tr class="mail_title"><td width="70%"><font size="+2">Send Mail</font></td><td width="15%"></td><td width="15%"></td></tr>
</table>
<?php
$user = $session->username;
print "<form action=\"/includes-functions/mailing.php?user=$user\" method=\"post\">";
?>
<table width="100%" border="0" cellspacing="0" cellpadding="4">
<tr>
<td class="<?php
if ($req_user_info['gender'] == 'Female'){ 
	print "mail_title_sub";
}
Else {
	print "mail_title_sub";

}
?>">
<?php
if ($req_user_info['username'] == $usrname){ 
    print("<input type=\"submit\" value=\"Send\"> | <a href=\"user_profile_mail.php?user=$usrname\">Back to inbox</a>"); 
}
Else {
}
?>
</td>
</tr>
</table>
<table width="100%" border="0" cellspacing="0" cellpadding="4">
<tr>
<td class="mail_title_sub">
To: <input type="text" name="to" />
</td>
<td class="mail_title_sub">
Subject: <input type="text" name="subject" />
</td>
</tr>
</table>
<table width="100%" border="0" cellpadding="0" cellspacing="0" >
<tr class="mail_title">
<td width="10%"></td>
<td width="80%">
<textarea name="post" rows="30" cols="80"></textarea>
</td>
<td width="10%"></td>
</tr>
</table>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td class="<?php
if ($req_user_info['gender'] == 'Female'){ 
	print "mail_title_sub";
}
Else {
	print "mail_title_sub";

}
?>">
Advertisement:
</td>
	</tr>
  <tr>
    <td class="<?php
if ($req_user_info['gender'] == 'Female'){ 
	print "mail_title_sub";
}
Else {
	print "mail_title_sub";

}
?>" align="center">
</td>
	</tr>
</table>

[mykg4orce]

to match the entered username to an existing one in the DB, you must do a query to the db:

$q = SELECT * FROM users WHERE username='$enteredUsername'

$result = mysql_query($q);

if (!$result) {
echo "incorrect username";
} else {
// do something positive
}

to validate any field you need the name of the field:

if (strlen($_POST['subject']) == 0) {
echo "please enter a subject";
}

strlen() gets the chr count of the field value. There are several different ways you can validate a field. There are entire classes that check if an email is bogus or not. Type something like, "field validation PHP" in google and you'll see what I mean. Here is one for example:
http://simonwillison.net/2003/Jun/17/theHolyGrail/

Just a note, hide your URLs. Someone with too much time on their hands can exploit what you are trying to build, especially when it involves grown-up babies...or grown-up acting like babies...watever