<?php
 
function is_even($num) {
    return is_int($num) && abs($num % 2) == 0;
}
function is_odd($num) {
    return is_int($num) && abs($num % 2) == 1;
}
// this last one seems self-explanatory, but if you want it, here it is
function is_neither_even_nor_odd($num) {
    return !is_even($num) && !is_odd($num);
}
 
// Tests: The following should all output true:
var_dump(
	is_even(0),
	is_even(2),
	is_even(-6),
	is_even(51238238),
	is_odd(1),
	is_odd(-1),
	is_odd(57),
	is_neither_even_nor_odd(1.5),
	is_neither_even_nor_odd(2.5),
	is_neither_even_nor_odd(-0.5),
	is_neither_even_nor_odd(0.00000001)
	);

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