Consider the following case. We have an array with identical keys.
$arr = array(1 => 10, 1 => 11);
What happens when the interpreter reaches this line of code? This is not a syntax error and it is completely valid. Very similar, but more interesting case is when we have an array of identical keys, where those identical keys are represented once as an integer and then as a string.
$arr = array(1 => 10, "1" => 11);
Now several questions arise. First of all, how many elements have this array? Two or one. This can be easily verified by checking what count() will return. Continue reading Thing to Know About PHP Arrays