16. strtoupper() and strtolower()

strtoupper() and strtolower(), which make your entire stringUPPERCASE or lowercase. Here is an example of each:

$uppercase = strtoupper($myname);
print $uppercase;
// prints "DAVID"

$lowercase = strtolower($uppercase);
print $lowercase;
// prints "david"

You can also call these functions on a string directly, like so:

print strtolower("David");
// prints "david"