What is the meaning of the system message, "Allowed memory size of <number> bytes exhausted"?

Given the following array: $array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red'); Which will print 2?

Should assert() be used to check user input?

Which is not a predefined constant?

Which regular expression can check the validity of an e-mail addresss?

What is 'empty()'?

Which is not a magic function in PHP?

Given this code: function doSomething( &$arg ) { $return = $arg; $arg += 1; return $return; } $a = 3; $b = doSomething( $a ); what is the value of $a and $b after the function call?

What's the output? '; echo is_finite(log(0)) . '
'; echo is_finite(2000); ?>

What's the output? $array1 = array('a' => 'green', 'b' => 'brown', 'c' => 'blue', 'red'); $array2 = array('a' => 'green', 'yellow', 'red'); $result = array_diff_assoc($array1, $array2); print_r($result);

Is it possible to initiate abstract class?