Convert a string to uppercase:

strtoupper() function is used to convert a string to uppercase. It convert all characters of string to uppercase.

Syntax:

strtoupper(string)

You have to pass only one parameter to the function i.e., the string which you want to convert to uppercase.

For example:

<?php
echo strtoupper("Convert this string to uppercase");
?>

Convert a string to lowercase:

strtolower() function is used to convert a string to lowercase. It convert all characters of string to lowercase.

Syntax:

strtolower(string)

You have to pass only one parameter to the function i.e., the string which you want to convert to lowercase.

For example:

<?php
echo strtolower("CONVERT THE STRING TO LOWERCASE");
?>