PHP English letter case conversion function

Example 1, convert the first letter of each word to uppercase: ucwords()

$foo = 'hello world!';
$foo = ucwords($foo); // Hello World!
$bar = 'HELLO WORLD!';
$bar = ucwords ($bar); // HELLO WORLD!
$bar = ucwords(strtolower($bar)); // Hello World!
?>

Example 2, the first letter of the first word changes Uppercase: ucfirst()

$foo = 'hello world!';
$foo = ucfirst($foo); // Hello world!
$bar = 'HELLO WORLD!';
$bar = ucfirst ($bar); // HELLO WORLD!
$bar = ucfirst(strtolower($bar)); // Hello world!
?>

Example 3, the first letter of the first word changes Lowercase: lcfirst()

$foo = 'HelloWorld';
$foo = lcfirst($foo); // helloWorld
$bar = 'HELLO WORLD!';
$bar = lcfirst($bar) ; // hELLO WORLD!
$bar = lcfirst(strtoupper($bar)); // hELLO WORLD!
?>
Change all letters to uppercase: strtoupper()
Change all letters to lowercase: strtolower()

The above introduces a total of five English letter case conversion functions, namely ucwords, ucfirst, lcfirst, strtoupper, and strtolower, each with its own use.