Getting a value by type="hidden" - php

Question

In my application I'm printing out searchresults. I want to use those searchresults to send an invite to become a member in that group. I'm printing out those userdata but I'm wondering how I can use those data into another function (sendInvite or something). I have to get the user_id of that people ($row['user_id'] but I don't know how I can get it. I'm thinking about type="hidden" but I never used it before.)
PRINT OUT
<div id="InviteGroupMembers">
<form action="<?php echo $_SERVER['PHP_SELF'] . "?group_id=" .$group_id; ?>" method="post">
<div >
<input type="text" name="btnSearch" placeholder="Add people to group"/>
</div>
<div>
<button type="submit" name="">Add</button>
</div>
</form>
<form action="<?php echo $_SERVER['PHP_SELF'] . "?group_id=" .$group_id; ?>" method="post">
<?php
if (is_object($searchresult))
while ($row = $searchresult -> fetch_array()) {
echo "<div><p class='searchresults'><img src='uploads/" . $row['avatar'] . " " . "' alt='' />" . $row['surname'] . " " . $row['name'] . " " . "<input type='submit' name='btnAddMember'class='addFriendToGroup' value='' /><input type='hidden' name='user_id' value='" . $row['user_id'] . "'/></p></div>"; }
?>
</form>
</div>
PHP
if (isset($_POST["btnSearch"])) {
try {
$searchinput = mysql_real_escape_string($_POST['btnSearch']);
$searchresult = $user -> Search($searchinput);
} catch(exception $e) {
$feedback = $e -> getMessage("no results");
}
}
if (isset($_POST["btnAddMember"])) {
try{
$group_receiver_id = mysql_real_escape_string($_POST['user_id']);
var_dump($group_receiver_id);
}
catch(exception $e) {
$feedback = $e -> getMessage("no results");
}
}

Answer 1

input type hidden would work for you in this instance. The output below is based on it being within php code. Other wise you will need to use php tags within the value attribute.
<input type="hidden" name="user_id" value="$row['user_id']"/>
Then you can just get the post variable on form submission