<?php
session_start();
echo '<form name="enter" action="index.php" method="post"><input type="text" name="name2"><br><input type="password" name="pass2"><br><input type="submit" name="enter"></form>
<a href="index.php?page=reg">зарегаться</a><br>';
include_once('config.php');
if(isset($_POST['name2']))
{
$name2 = $_POST['name2'];
$pass2 = $_POST['pass2'];
$res = mysql_query("SELECT * FROM users WHERE name='$name2'",$db);
$row = mysql_fetch_assoc($res);
if($pass2==$row['pass']) echo $row['name']."<br>".$row['famil'];

$username = $row['name'];
$_SESSION['username'] = "$username";
}

if(isset($_GET['page']) and $_GET['page']='reg')
{
echo '<form name="reg" action="index.php?page=reg" method="post"><input type="text" name="name"><br><input type="text" name="fam"><br><input type="password" name="pass"><br><input type="submit" name="sub"></form>';

if(isset($_POST['name']))
{
$name = $_POST['name'];
$pass = $_POST['pass'];
$fam = $_POST['fam'];
$insert = mysql_query("INSERT INTO users (`name`,`famil`,`pass`) VALUES ('".$name."','".$fam."','".$pass."')",$db);
if($insert='true') echo "yes";
}
}

 $name2 = !empty($_GET['name2']) ? $_GET['name2'] : NULL

$res = mysql_query("SELECT * FROM users WHERE name='$name2'",$db);
$row = mysql_fetch_assoc($res);

$res = mysql_query("SELECT `id` FROM `users` WHERE name='$name2' AND '$pass2'",$db);
$row = mysql_fetch_assoc($res);