// strlen( ) is a built-in function that returns the length of a string
$length = strlen("PHP"); // $length is now 3
// sin() and asin( ) are the sine and arcsine math functions
$result = sin(asin(1)); // $result is the sine of arcsin(1), or 1.0
// unlink( ) deletes a file
$result = unlink("functions.txt"); // false if unsuccessful

In the first example, we give an argument, `"PHP"`,
to the function `strlen( )`, which gives us the
number of characters in the string it's given. In
this case, it returns `3`, which is assigned to the
variable `$length`. This is the simplest and most
common way to use a function.