Search for highest key/index in an array

How can I get the highest key/index in an array with php? I know how to do it for the values.

E.g.: from this array I would like to get 10 as an integer value:

$arr = array(1 => "A", 10 => "B", 5 => "C");

I know how I could code it but I was asking myself if there is a function for this as well.

Answer

This should work fine

$arr = array( 1 => "A", 10 => "B", 5 => "C" );
max(array_keys($arr));