总是说输入是字母数字，除非我什么都不提交

Question

Here is a code. Whenever I submits anything the output says it's alphanumeric help me to get out of here.

<?php

$string ="$_POST[in]";

if(ctype_alnum($string)) 
{
echo "'{$string}' is alphanumeric!";
} else {
echo "'{$string}' is NOT alphanumeric!";
}

?>
<form action="alphanum.php" method="post">
<h1>Make Input:<input name="in"><span><input type="submit" value="Check"></span></h1>
</form>

Answer 1

What you need is ctype_alpha, this checks if the text enterd is alphabet only or it has numbers where as, ctype_alnum checks for both numbers and alphabets and considers both as alphanumeric

<?php
if (isset($_POST['in'])) {
    $string =$_POST['in']; // validate / sanitize here

    //$string = "(*&";
    if(ctype_alpha($string))
    {
        echo "'{$string}' is NOT alphanumeric!";
    } else {
        echo "'{$string}' is alphanumeric!";
    }
}


?>
<form action="test.php" method="post">
    <h1>Make Input:<input name="in"><span><input type="submit" value="Check" name="check"></span></h1>
</form>