<?php
$hostname_strcn = "localhost";
$database_strcn = "basededatos";
$username_strcn = "usuario";
$password_strcn = "";
mysqli_connect($hostname_strcn, $username_strcn, $password_strcn) or
die(mysqli_error());
mysqli_select_db($database_strcn) or die(mysqli_error());
?>

<?php
if (isset($_GET['action'])) {

include_once('connect.php');

$strsql = "SELECT * FROM paciente WHERE codigo_pac=".$_GET['codigo_pac'];
$rs = mysqli_query($strsql) or die(mysqli_error());
$row = mysqli_fetch_assoc($rs);
$total_rows = mysqli_num_rows($rs);

}

?>

<div>
    <div class="form-group">
            <label for="first-name">Ingrese el Código del Paciente</label>
            <input type="text" class="form-control" id="codigo_pac" value="<?php echo($row['codigo_pac']);?>" name ="codigo_pac">
            <input type="hidden" id="action" name="action" value="sent">
            <input type="submit" id="btn_submit" value="Enviar">
        </div>

        </div>
<div class="form-group">
            <label for="first-name">Nombres</label>
            <input type="text" class="form-control" id="nom" name ="nom" value="<?php echo($row['nombre']); ?>">
        </div>
        <div class="form-group">
            <label for="last-name">Apellido Paterno</label>
            <input type="text" class="form-control" id="apat" name ="apat" value="<?php echo($row['apellido_paterno']); ?>">
        </div>