$s = "Let's dance the macarena";

$word = "dance";
$ok = index($s,$word) >= 0;
print($ok ? "YES\n" : "NO\n");

$word = "car";
$ok = index($s,$word) >= 0;
print($ok ? "YES\n" : "NO\n");

$word = "duck";
$ok = index($s,$word) >= 0;
print($ok ? "YES\n" : "NO\n");

YES
YES
NO