count

Returns the number of elements in an array.

PHP

$a = array('first' => 1, 'second' => 2);
echo count($a);
// => 2

Ruby

my_array = [1, 2];
puts my_array.length;
# => 2

sizeof

The sizeof() function is only an alias of count, which returns the number of elements in an array.

For further information about sizeof(), see count().