values sent with POST/GET will not print as variables - php

Question

I am working on a project to take two submitted variables and turn them into php variables (eventually they will multiply together) but as of now I cannot get the variables to be treated as such/echo.
I tried changing from POST to GET and the variables are sent through (appear in query line) but they don't print on the page
<?php
if (isset($_POST['submit'])) {
echo $_POST['length'];
echo $_POST['numPass'];
}
?>
<form method="post" action="">
<input type="number" name="length">
<input type="number" name="numPass">
<input type="submit">
</form>
I expect that the variables will be echoed as a regular statement.
ie. length=2 and numPass=4
24

Answer 1

You can get the $_GET and $_POST request using $_REQUEST
if (isset($_REQUEST['submit'])) {
echo $_REQUEST['length'];
echo $_REQUEST['numPass'];
}
<form method="post" action="">
<input type="number" name="length">
<input type="number" name="numPass">
<input type="submit" value="submit">
</form>

Answer 2

$POST['submit'] does not exist because your submit button does not have a name, it needs a name the same as your other inputs

Answer 3

It is better to check the input to avoid possible errors. You can try its example:
<?php
if( $_POST["length"] && $_POST["numPass"] ) {
echo "1: " . $_POST['length'] . "<br>";
echo "2: " . $_POST['numPass'] . "<br>";
echo $_POST['length'] * $_POST['numPass'];
}
?>
<form method="post" action = "<?php $_PHP_SELF ?>">
<input type="number" name="length">
<input type="number" name="numPass">
<input type="submit">
</form>