Why does the array_search function fail?

Question

PHP

There is an array like $alphabet = array('а', 'б', 'в', 'г', 'д').
I want to get the element key array_search('а', $alphabet)
Why does this code return an error?

<b>Warning</b>:  array_search() [<a href='function.array-search'>function.array-search</a>]: Wrong datatype for second argument in...

Answer 1

stackoverflow.com/questions/11708203/array-search-...

Answer 2

I can assume that indices are needed (0 => 'a', 1 => 'b')