怎样把每一页的数据条数改为4条

现在每一页的数据条数是两条

我想改为四条，但是我又看不太懂这个代码，使用的是Dreamweaver这个编译器，学的是PHP，这个应该怎样修改代码啊，下面是代码

session_start();

require "conn.php";

// 判断是否登录
@session_start();
if(!isset($_SESSION['aname'])) {
header("location: login.php");die;
}

$cond = " where 1=1 ";

if(!empty($_POST['name'])) {
$name = $_POST['name'];
$cond .= " and name like '%{$name}%' ";
}

// 实现分页
$num = 2;
$res = mysqli_query($conn, "select count(*) as total from tushu $cond");
$row = mysqli_fetch_array($res);
$total = $row['total'];

if($total == 0) {
$pages = 1;
} else if($total % $num == 0) {
$pages = $total / $num;
} else {
$pages = (int)($total/$num) + 1;
}

// 获取当前页数
$page = isset($_GET['p']) ? $_GET['p'] : 1;

// 计算偏移量
$pianyi = ($page - 1) * $num;

$res = mysqli_query($conn, "select * from tushu $cond order by id desc limit $pianyi,$num");

?>

 include "header.php"; ?>

    
    <div class="fr righter">
      <div class="title">
       图书列表
      div>

    <table>
        
        <tr>
            <th>ISBNth>
            <th>书名th>
            <th>出版社th>
            <th>存量th>
            <th>位置th>
            <th>操作th>
        tr>
         while($row = mysqli_fetch_array($res)): ?>
        <tr>
            <td> echo $row['isbn']; ?>td>
            <td> echo $row['name']; ?>td>
            <td> echo $row['chubanshe']; ?>td>
            <td> echo $row['cunliang']; ?>td>
            <td> echo $row['location']; ?>td>
            <td>
                
                    if($_SESSION['role'] == "用户"):
                ?>
                <a href='jieyue.php?id= echo $row['id']; ?>'><button>借阅<^tton>a>
                 endif; ?>

                
                    if($_SESSION['role'] == "管理员"):
                ?>
                <a href='tushuEdit.php?id= echo $row['id']; ?>'><button>编辑<^tton>a>
                <a href='tushuDel.php?id= echo $row['id']; ?>'><button>删除<^tton>a>
                 endif; ?>
            td>
        tr>
         endWhile; ?>
        
        <tr>
            <td style="text-align: center;" colspan="6">

                总条数目： echo $total; ?>
            
                 if($page != 1): ?>
                    <a href="./tushuList.php?p=1">首页a> 
                 else: ?>
                    首页
                 endif; ?>

                 if($page != 1): ?>
                    <a href="./tushuList.php?p= echo $page-1; ?>">上一页a> 
                 else: ?>
                    上一页
                 endif; ?>

                 if($page != $pages): ?>
                    <a href="./tushuList.php?p= echo $page+1; ?>">下一页a> 
                 else: ?>
                    下一页
                 endif; ?>

                 if($page != $pages): ?>
                    <a href="./tushuList.php?p= echo $pages; ?>">尾页a> 
                 else: ?>
                    尾页
                 endif; ?>

            td>
        tr>
    
    table>

  div>

// 实现分页
$num = 2; 这里改成4就可以了