Search for highest key/index in an array

Question

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

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

Answer 1

This should work fine

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