【紧急】php for循环和数组的奇怪问题

<?php
for($i=1;$i<=5;$i++){
    $block = 8.0+(0.5*$i-0.5);
    $time[$block]=$block;

}
echo"<pre>";
print_r ($time);
?>

Array
(
    [8] => 8.5
    [9] => 9.5
    [10] => 10
)