Floating point values have a limited precision. Hence a value might 
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly 
printing it without any mathematical operations.

If you would like to know more about "floats" and what IEEE
754 is read this:
http://docs.sun.com/source/806-3568/ncg_goldberg.html
 
Thank you for your interest in PHP.

.

i change the code,like this:

<?php
$t = 1000-182.41;
$t = $t;
$b = 817.59;

var_dump( $t );
var_dump( $b );
var_dump( $t*100 );
var_dump( ceil( $t*100 ) );

if ( $t == $b )
	echo '$t == $b';
else
	echo '$t != $b';

?>


result:
=============

float(817.59)
float(817.59)
float(81759)
float(81759)
$t == $b

ths result is i want,is true