PHP Performing Calculations with Multidim Array - php

Question

I've currently have a multidim array with a planet and it's relative gravity value.
([0][0] = planet and [0][1] = relative gravity).
On my page I have a form where the user submits the weight of an item and the planet they wish to see it's weight on. What I'm trying to do is take the weight the user entered and multiply it by the relative gravity of the specific planet they chose.
My initial attempts have been to use something like this:
<?php
$file = fopen("PLANET.txt", "r");
$planets = array();
while(!feof($file)) {
$line = fgets($file);
$value = explode(" ", $line);
array_push($planets, $value);
}
if(isset($_POST['weight']) && isset($_POST['planet'])) {
while($x=0;x<count($planets);x++) {
if($_POST['planet'] == $planets[x][0]) {
$final_weight = $_POST['weight'] * $planets[x][1];
}
}
}
?>
However it does not seem to be working... I am brand new to PHP and I could be making a dumb mistake but I can't seem to find it, any help would be much appreciated.
EDIT:
Ok here is what I have now and it seems to be working, thank you guys very much. Feel so dumb for making those mistakes!
for($x=0;$x<count($planets);$x++) {
if($_POST['planet'] == $planets[$x][0]) {
$final_weight = $_POST['weight'] * $planets[$x][1];
}
}

Answer 1

Your while loop should look like that (note the additional $ signs):
while($x=0;$x<count($planets);x++) {
if($_POST['planet'] == $planets[$x][0]) {
$final_weight = $_POST['weight'] * $planets[$x][1];
}
}
EDIT: The above is complete nonsense. No idea what got into me. It should of course be:
for($x=0;$x<count($planets);x++) {
if($_POST['planet'] == $planets[$x][0]) {
$final_weight = $_POST['weight'] * $planets[$x][1];
}
}