$odin = substr($query, 0, 3);		
$dva = substr($query, 4, 6);

urce i
Res

$result = mysql_query("SELECT * FROM table");
while ($row = mysql_fetch_array($result, MYSQL_BOTH)) {
		$odin = substr($row['nomer'], 0, 3);
		$dva = substr($row['nomer'], 4, 6);
		echo '<p>'.$dva.'</p>';
		echo '<p>'.$odin.'</p>';
}

if (strlen($summa_pervich_trex_chisel) = 1 and strlen($summa_vtorix_trex_chisel) = 1)
	{
		if($summa_pervich_trex_chisel = $summa_vtorix_trex_chisel)
			{
				$a = 1;
			}
			else $a = 0;
	}

Fatal error: Can't use function return value in write context in C:\xampp\htdocs\dob2.php on line 71

if (strlen($summa_pervich_trex_chisel) = 1 and strlen($summa_vtorix_trex_chisel) = 1)

if (strlen($summa_pervich_trex_chisel) == 1 and strlen($summa_vtorix_trex_chisel) == 1)
	{
		if($summa_pervich_trex_chisel == $summa_vtorix_trex_chisel)
			{
				$a = 1;
			}
			else $a = 0;
	}

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in C:\xampp\htdocs\new\authmain.php on line 82

if (mysql_num_rows($query) == 1)

<?php
	
		if(isset($_POST['user']) && isset($_POST['pass']))
		{
		$userid = $_POST['user'];
		$password = $_POST['pass'];
		
		@ $db = mysql_connect('localhost', 'root', '24011993', 'site');
	  	mysql_select_db(site) or die(mysql_error());
	  
	  	$query = ("select * from user where user='$userid' and password=sha1('$password') LIMIT 1");
		if (mysql_num_rows($query) == 1)
		{
		session_start();
		$_SESSION['valid_user'] = $userid;
		}
		
		}
		
		?>
        <?php 
		if (isset($_SESSION['valid_user']))
		{
		echo 'Вы вошли как '.$_SESSION['valid_user'].'';
		echo '<a herf="logout.php">Выход</a>';
		}
		else
		{
			if (isset($userid))
			{
			echo 'Извините но вход невозможен';
			}
			else
			{
			echo 'Вы еще не вышли из системы';
			}
		}
		?>

if (mysql_num_rows($query) == 1)

if (mysql_num_rows($query) != "" )

$query = mysql_query("SELECT * FROM user WHERE user='$userid' and password=sha1('$password') LIMIT 1");
if (mysql_num_rows($query) != "")

$query = ("SELECT * FROM user WHERE user='$userid' and password=sha1('$password') LIMIT 1");

mysql_query

$query = mysql_query("SELECT * FROM user WHERE user='$userid' and password=sha1('$password') LIMIT 1");

password=sha1('$password')

password='$password'

$query = mysql_query("SELECT * FROM user WHERE user='$userid' and password='$password' LIMIT 1");