Php / Basics / Integers / Decimal 2 Ocatal - https://www.minte9.com/php/basics-integers-13

index.php

<?php

/**
 * Compose $m octal value using myFunc() recursively
 * Use reminder and quontient values
 *
 * 97 (decimal) = 141 (octal)
 * 97 % 8 => reminder 1
 * 12 % 8 => reminder 4
 * 1  % 8 => reminder 1
 * 
 * 1*8^2 + 4*8^1 + 1*8^0 = 64 + 32 + 1 = 97
 */

function myFunc($no) {
    
    /**
     * SOLUTION
     */
    if ($no == 0) return NULL;

    $m = $no%8; // reminder
    $q = (int) $no/8; // quontient
    $m = myFunc($q) . $m;

    return (int) $m;
}

// TESTS
{
    foreach([7=>7, 8=>10, 10 => 12, 97 => 141] as $k=>$v) {
        if (myFunc($k) != $v) throw new Exception($k . " failed");
        if (decoct($k) != $v) throw new Exception($k . " failed");
    }
    echo "Tests passed!";
}