Uncaught error call to undefined function mysql_num_rows()

<?php

$link = mysql_connect("localhost", "user", "password", "database");
/* check connection */
if (!$link) {
die ('could not connect: ' . mysql_error());
}
else {
printf("name to find " .$_POST["name"]."<br />");
$name_search_sql="SELECT * FROM tbl_guests WHERE guestname = '".$_POST['name']."'";
$name_search_res=mysql_query($name_search_sql) or die(mysql_error($mysql));
if (mysql_num_row($name_search_res) < 1) {
printf("noname");
}
else {
while ($new = mysql_fetch_array($name_search_res)) {
$new_name=$new['guest_name'];
printf("name: ".$new_name);
}
}
/* close connection */
mysql_close($link);
}
?>