Problem with bcmath in php

<?php
$tot=fgets(STDIN);
$m=fgets(STDIN);
echo bcsub($tot,$m);
?>

inputs:
10
2
output
0

but this

<?php
$tot='10';
$m='2';
echo bcsub($tot,$m);
?>

gives proper output:
8

and in both cases, $tot and $m are strings,
why does this happen and how do i fix it?