isset

<?php
$myHost = "localhost";
$myUser = "root";
$myPass = "";
$myDbs = "siswadb";

//Konek ke server MySQL
$koneksiDbs = mysql_connect($myHost, $myUser, $myPass)
              or die("Gagal koneksi...!").mysql_error();

//Buka database siswadb
mysql_select_db($myDbs)
or die("Database $myDbs tidak ada").mysql_error();

if($_GET){
    //Baca variable URL (browser)
    $IdJurusan = $_GET['id'];

    //Baca data didalam tabel jurusan sesuai ID yang didapat
    $sql = "SELECT * FROM jurusan
           WHERE id_jurusan = '$IdJurusan'";
    $query = mysql_query($sql, $koneksiDbs)
             or die("Query salah : ").mysql_error();
    $data = mysql_fetch_array($query);}
?>
<html>
<head>
<title>Ubah Jurusan</title>
</head>
<body>
<form name="form1" method="post" action="jurusanUbahSave.php">
    <table width="600" border="0" cellpadding="1" cellspacing="2">
        <tr>
            <td colspan="2" bgcolor="FFFFCC"><b>TAMBAH JURUSAN</b></td>
        </tr>
        <tr>
            <td width="107"><b>Nama Jurusan</b></td>
            <td width="483">:
            <input name="txtNmJurusan" type="text"
            value="<?php isset($data['nm_jurusan'])?echo $data['nm_jurusan']:echo ''; ?>" size="50" maxlength="60">
            <input name="txtIdJurusan" type="hidden"
            value="<?php echo isset($data['id_jurusan'])?$data['id_jurusan']:''; ?>"></td>
        </tr>
        <tr>
        <td>&nbsp;</td>
        <td><input type="submit" name="Submit" value="Simpan"></td>
        </tr>
    </table>
</form>
</body>
</html>