Simple Prime number program in PHP

Que: What is Prime number?
Ans: A number is prime if it is divisible only by one and itself. (Ex: 2, 3, 5, 7, 11, 13, 17....etc)

Program:

<?php
$num = 4; // <=== Replace desired number to check
for ($i = 2; $i <= $num - 1; $i++) {
    if (bcmod($num, $i) == 0) {
        echo $num . " is not prime number :(";
        break;
    }
}
if ($num == $i)
    echo $num . " is prime number :)";
?>