验证:似乎忽略了字母字符不是数字的事实

根据标题，当用户在两个计算字段中的任何一个中输入恶意输入（不是1或0）时，我在二进制计算器中遇到触发错误的问题。

输入应限制为1或0。为什么当我输入"a"时，计算仍会继续？

$submit = htmlspecialchars(strip_tags(stripslashes($_POST['submit'])));
$val1 = htmlspecialchars(strip_tags(stripslashes($_POST['val1'])));
$val2 = htmlspecialchars(strip_tags(stripslashes($_POST['val2'])));
$val1_length = strlen($val1);
$val2_length = strlen($val2);
$val1 = array_reverse(str_split($val1, 1));
$val2 = array_reverse(str_split($val2, 1));
// Val 1 - Checking
$count = 0; // count variable counts how many times the loop recurs and stops it appropriately
while ($count < $val1_length) {
if(($val1[$count] != 0) && ($val1[$count] != 1) && (is_numeric($binary_input))) { // checks if input is comprised of 0 or 1
    showInputError();   
    exit(); // input does not contain 0 or 1, abort script and do not attempt further calculations
}
$count = $count + 1; // increment the count variable after one successful loop
} // Val1 was fine