求助：关于php一段简单代码

这是php和mysql web开发书中一个例子，目的就是把文件保存的订单信息炸开，用表格显示。我运行时为什么只显示表头，没有表格数据呢。
orders.txt中就是订单信息，用Tab分隔的，已正确读取到$orders中。貌似是后边的for循环中有问题。

Bob's Auto Parts

Customer Orders

//Read the entire file
//Each order becomes an element in the array
$orders = file("./orders.txt");

//count the number of orders in the array$number_of_orders = count($orders);if($number_of_orders = 0) {    echo "
No orders pending. Please try again later.
";}echo "\n";echo "";for($i = 0; $i < $number_of_orders; $i++) {    //Split up each line    $line = explode("\t", $orders[$i]);    //keep only the number of items ordered    $line[1] = intval($line[1]);    $line[2] = intval($line[2]);    $line[3] = intval($line[3]);    //output each other     echo "";}echo "
Order Date
          
Tires
          
Oil
          
Spark plugs
          
Total
          
Address
      
            
".$line[0]."
            
".$line[1]."
            
".$line[2]."
            
".$line[3]."
            
".$line[4]."
            
".$line[5]."
          
";

?>