if (empty($birnima['oddiy'])) {
        header ('location: '.HOST.'/sahifa/');
    }

<?php
$login = $_POST['login'];
$parol = $_POST['parol'];
if ($login == "admin" && $parol == "admin") {
    echo 'Login parol to\'g\'ri kiritilsa bu matn ko\'rinadi';
} else {
    if (isset($_POST)) { echo '
        <form method="POST" action="bu_kod_yozilgan_sahifa.php">
            login<br /><input type="text" name="login"></input><br/>
            parol<br /><input type="password" name="parol"></input><br/>
            <input type="submit" name="submit" value="Kirish"></input>
        </form>';
    }
}
?>

if ($test) 
    echo 'test bor';
else
    echo 'test yo\'q';
echo 'bu matn endi if else ga umuman aloqasi yo\'q';

if ($test) {
    echo 'test bor';
} else {
    echo 'test yo\'q';
    echo 'rostdan ham test yo\'q';
    echo 'test yo\'q, birinchi testni siz yarating';
}
echo 'endi bu matn if else ga aloqor emas!';

if(isset($_GET['go'])){
echo 'Siz goo manzilidasiz!';
}else{
echo 'Siz bosh saxifadasiz';
}

if(isset($_GET['go']))
echo 'Siz goo manzilidasiz!';
else
echo 'Siz bosh saxifadasiz';

<?php
$a=2;
if ($a<5){ echo '5 dan kichik';} else {echo '5 dan kichik emas.';}
?>

<?php
$a=2;
if ($a<5){ echo '5 dan kichik';} echo '5 dan kichik emas.';
?>