<form action="" method="post">
<input type="text" name="a[]" />
<input type="text" name="a[]" />
<input type="submit" />
</form>
<?php echo $_POST['a'][1]; echo $_POST['a'][0];?>
<form action="" method="post">
<input type="text" name="a[]" />
<input type="text" name="a[]" />
<input type="submit" />
</form>
<?php echo $_POST['a'][1]; echo $_POST['a'][0];?>