用数组中的内容替换字符串中的内容

Question

I am making a filter for strings that will filter out any words in the string that are found in the array with the number sign "#". It just doesn't seem to work.

Here are my url parameters: http://www.mydomain.com/test.php?str=Noob%20no

<?php
    $blacklist = array("noob","yes");
    $t = "";
    $str = explode(" ",strtolower($_GET["str"]));
    foreach ($str as $i) {
        $s = str_replace($i, str_repeat("#", strlen($i)), $blacklist);
        $t = $t . $s[0];
    }

    echo $t;
?>

This is what it outputs for "noob no:"

######ob

where it should echo something like this:

#### no

Answer 1

$blacklist = array("noob","yes");
$t = "";
$str = explode(" ",strtolower("Noob no"));
foreach ($str as $i) {
    if ( in_array($i,$blacklist) ) {
       $i = str_repeat('#',strlen($i));
    }
    $t = $t . $i . " ";
}

echo $t;