php数字比较出错

if (is_numeric($a) && is_numeric($b)) {
    if ($a == $b) {
        echo "Numbers are equal.";
    } else {
        echo "Numbers are not equal.";
    }
} else {
    echo "One or both values are not numeric.";
}

$epsilon = 0.00001;
if (abs($a - $b) < $epsilon) {
    echo "Numbers are approximately equal.";
} else {
    echo "Numbers are not equal.";
}

$hexNumber = "1A";
$decimalNumber = hexdec($hexNumber);

if ($decimalNumber == 26) {
    echo "Numbers are equal.";
} else {
    echo "Numbers are not equal.";
}