Checking the Remainder of Division in PHP

Let we have two variables with numbers:

<?php
	$a = 10;
	$b = 3;
?>

Let's find the remainder of dividing one variable by another:

<?php
	$a = 10;
	$b = 3;
	
	echo $a % $b; // outputs 1
?>

Now let the variables store such values that one variable is divisible by the second without a remainder:

<?php
	$a = 10;
	$b = 5;
	
	echo $a % $b; // outputs 0
?>

Let's write a script that will check whether one number is divisible by the second without a remainder:

<?php
	$a = 10;
	$b = 3;
	
	if ($a % $b === 0) {
		echo 'divisible without remainder';
	} else {
		echo 'divisible with remainder';
	}
?>

Now let it be required, if the number is divisible with a remainder, to display this remainder on the screen:

<?php
	$a = 10;
	$b = 3;
	
	if ($a % $b === 0) {
		echo 'divisible without remainder';
	} else {
		echo 'divisible with remainder ' . $a % $b;
	}
?>

In the code above, it turns out that the remainder is calculated in two places, which is not optimal.

Let's fix the problem:

<?php
	$a = 10;
	$b = 3;
	$rest = $a % $b;
	
	if ($rest === 0) {
		echo 'divisible without remainder';
	} else {
		echo 'divisible with remainder ' . $rest;
	}
?>

As you know, even numbers are divisible by 2 without a remainder, and odd numbers - with a remainder. Let you are given a number. Using the operator % and the if construction, check if it is even this number or not.

Given a number. Check that it is divisible by 3.