How to change upper to lowercase,lower to uppercase,firstletter to upper case in php?

<?php
$foo = 'welcome';
$foo = ucfirst($foo);            

//Output

Welcome

$bar = 'WELCOME!';
$bar = ucfirst($bar);              // WELCOME
$bar = ucfirst(strtolower($bar));

//Output
 Welcome

?>


<?php
$str = "Php Scripts Here";
$str = strtolower($str);
echo $str;

//Output
 php scripts here

?>

<?php
$str = "Php Scripts Here";
$str = strtoupper($str);
echo $str;

// Output
PHP SCRIPTS HERE
?>