rand_c.php

<?php
define('CIRCLE_D', 36);

for ($k = 0; $k < 100; $k++):

    list($px, $py) = get_rand_circle(CIRCLE_D / 2);
for ($i = 0; $i < CIRCLE_D;$i++) {
    for ($j = 0; $j < CIRCLE_D;$j++) {
        if ($i == $py && $j == $px) {
            echo '=';
        }
        else {
            echo is_circle(CIRCLE_D / 2 - $i, CIRCLE_D / 2 - $j, CIRCLE_D / 2) ? ' ' : '*';
        }
    }
    echo PHP_EOL;
}

endfor;

function is_circle($x, $y, $r) {
    return (pow($x, 2) + pow($y, 2) < ($r * $r));
}

function get_rand_circle($r)
{
    $i = 0;
    do {
        $px = rand(0, $r * 2);
        $py = rand(0, $r * 2);
        if ($i++ > 100) return;
    } while(!is_circle($r - $px, $r - $py, $r));
    return array($px, $py);
}