PHP-Rechenoperationsmethode

<form action="index.php" method="post">
请输入你的课程的数量:<input type="text" name="course_number"/><br/>
<input type="submit" value="submit"/>
</form>

<?php session_start();
  $course_number=$_POST["course_number"];
  $_SESSION["course_number"]=$course_number;
  $m=0;
  echo "<form action=&#39;result.php&#39; method=&#39;post&#39;>";
  for($i=0;$i<$course_number;$i++):?>
  分数:<input type="text" name="<?php echo "course".$i;?>" />-------学分(权重):<input type="text" name="<?php echo "credit".$i;?>" /><br/><br/>
  <?php 
  endfor;
  echo "<input type=&#39;submit&#39; value=&#39;submit&#39;>";
  echo "</form>"."<br/>";
?>

<?php session_start();
  $score=array();
  $balance=array();
  $sum=0;
  $total_score=0;
  $result=0;
  for($i=0;$i<$_SESSION["course_number"];$i++)
  {
    $score[$i]=$_POST["course".$i];
  }
  for($i=0;$i<$_SESSION["course_number"];$i++)
  {
    $balance[$i]=$_POST["credit".$i];
  }
  for($i=0;$i<$_SESSION["course_number"];$i++)
  {
    $sum=$sum+$score[$i]*$balance[$i];
  }
  for($i=0;$i<$_SESSION["course_number"];$i++)
  {
    $total_score=$total_score+$balance[$i];
    echo $total_score."<br>";
  }
  $result=$sum/$total_score;
  echo "您的加权平均为:".$result;
?>