$items = [];
// ...
if (count($items) > 0) {
 foreach ($items as $item) {  // process on $item ...
 }}

$items = [];
// ...
foreach ($items as $item) { // process on $item ...
}

function foo(User $user) {
 if (!$user->isDisafunction foo(User $user) {
 if (!$user->isDisabled()) {
  // ...
  // long process
  // ...
 }
}bled()) {
  // ...
  // long process
  // ...
 }
}

function foo(User $user) {
 if ($user->isDisabled()) {
  return;
 } // ...
 // long process
 // ...
}

$a = null;
$b = null;
$c = null;
// ...

if (!isset($a) || !isset($b) || !isset($c)) {
 throw new Exception("undefined variable");
}

// or

if (isset($a) && isset($b) && isset($c) {
 // process with $a, $b et $c
}

// or 

$items = [];
//...
if (isset($items['user']) && isset($items['user']['id']) {
 // process with $items['user']['id']
}

$a = null;
$b = null;
$c = null;
// ...

if (!isset($a, $b, $c)) {
 throw new Exception("undefined variable");
}

// or

if (isset($a, $b, $c)) {
 // process with $a, $b et $c
}

// or 

$items = [];
//...
if (isset($items['user'], $items['user']['id'])) {
 // process with $items['user']['id']
}

$name = "John Doe";
echo sprintf('Bonjour %s', $name);

$name = "John Doe";
printf('Bonjour %s', $name);

$items = [
 'one_key' => 'John',
 'search_key' => 'Jane',
];if (in_array('search_key', array_keys($items))) {
 // process
}

$items = [
 'one_key' => 'John',
 'search_key' => 'Jane',
];if (array_key_exists('search_key', $items)) {
 // process
}

if (isset($items['search_key'])) {
 // process
}