关于在html中插入php代码

Question

我有一个登录页面如下 为什么在一个li里面插入一段php代码来显示错误信息、但在运行的时候会提示
Parse error: syntax error, unexpected '<' in E:\php\index.php on line 
百思不得其解、应该怎么连接呢？<?php
require("db/db_connect.php");
if ($_POST)
{
extract($_POST);
      $sql = "select * from useraccount where username='$username' and password='$password'";
      $result = mysql_query($sql,$conn);
      $rows = mysql_num_rows($result);
        if ($rows)
         {
          session_start();
          $_SESSION['user'] = $username;
          header("location:home.php");
          }
          else
          {
           session_start();
           $_SESSION['error']= "用户名密码错误";
         }
  }
echo '<div id="main">
  <div id="wrapper">
    <form action="index.php" method="Post" id="form1" >
      <div id="sys_name">信息管理系统</div>
      <ul id="cont">
        <li>
          <label class="lb" for="uname">用户名</label>
          <input name="username" id="uname" type="text" class="ip" value="请输入用户名" maxlength="18" />
        </li>
        <li>
          <label class="lb" for="pwd">密码</label>
          <input name="password" id="pwd" type="password" class="ip" value="" maxlength="10" />
        </li>
        <li><span>
          <input  type="image" name="login" src="images/ente.png" title="登录系统" onclick="return check_login()"/>
          </span></li>
          <li style="color:red;">'.<?php
          if(isset(($_SESSION['error']))
           echo $_SESSION['error']; 
          ?>.'</li>
      </ul>
      <p id="copy">Copyright @2011 Hangzhou Wangjing Co;LTD All rights reserved </p>
    </form>
  </div> 
</div>';
?>

Answer 1

if(isset(($_SESSION['error']))
多了个左括号

Answer 2

<?php
    require("db/db_connect.php");
        if ($_POST)
        {
            extract($_POST);
      $sql = "select * from useraccount where username='$username' and password='$password'";
      $result = mysql_query($sql,$conn);
      $rows = mysql_num_rows($result);
        if ($rows)
         {
             session_start();
          $_SESSION['user'] = $username;
             header("location:home.php");
             }
             else
             {
           session_start();
           $_SESSION['error']= "用户名密码错误";
         }
  }
    echo '<div id="main">
  <div id="wrapper">
    <form action="index.php" method="Post" id="form1" >
      <div id="sys_name">信息管理系统</div>
      <ul id="cont">
        <li>
          <label class="lb" for="uname">用户名</label>
          <input name="username" id="uname" type="text" class="ip" value="请输入用户名" maxlength="18" />
        </li>
        <li>
          <label class="lb" for="pwd">密码</label>
          <input name="password" id="pwd" type="password" class="ip" value="" maxlength="10" />
        </li>
        <li><span>
          <input  type="image" name="login" src="images/ente.png" title="登录系统" onclick="return check_login()"/>
          </span></li>
          <li style="color:red;">';?><?php
          if(isset(($_SESSION['error']))
              echo $_SESSION['error'].' 
          </li>
      </ul>
      <p id="copy">Copyright @2011 Hangzhou Wangjing Co;LTD All rights reserved </p>
    </form>
  </div> 
</div>';
?>

Answer 3

php标记未结束前不能在内部再次书写php开始标记<?php
    require("db/db_connect.php");
        if ($_POST)
        {
            extract($_POST);
      $sql = "select * from useraccount where username='$username' and password='$password'";
      $result = mysql_query($sql,$conn);
      $rows = mysql_num_rows($result);
        if ($rows)
         {
             session_start();
          $_SESSION['user'] = $username;
             header("location:home.php");
             }
             else
             {
           session_start();
           $_SESSION['error']= "用户名密码错误";
         }
  }
    echo '<div id="main">
  <div id="wrapper">
    <form action="index.php" method="Post" id="form1" >
      <div id="sys_name">信息管理系统</div>
      <ul id="cont">
        <li>
          <label class="lb" for="uname">用户名</label>
          <input name="username" id="uname" type="text" class="ip" value="请输入用户名" maxlength="18" />
        </li>
        <li>
          <label class="lb" for="pwd">密码</label>
          <input name="password" id="pwd" type="password" class="ip" value="" maxlength="10" />
        </li>
        <li><span>
          <input  type="image" name="login" src="images/ente.png" title="登录系统" onclick="return check_login()"/>
          </span></li>
          <li style="color:red;">'.
          if(isset(($_SESSION['error']))
              echo $_SESSION['error'].'
          </li>
      </ul>
      <p id="copy">Copyright @2011 Hangzhou Wangjing Co;LTD All rights reserved </p>
    </form>
  </div> 
</div>';
?>