PHP用户登录系统实战教程中的问题

Question

原网页http://www.php.cn/code/3984.html

在第四步注册处理页面出现问题，注册页面点立即注册后调到注册处理页面报错

代码：

<?php  
session_start();
//注册处理界面 regcheck.php
    if(isset($_POST["hidden"]) && $_POST["hidden"] == "hidden")  
    {  
        $user = trim($_POST["username"]);//trim()函数移除字符串两侧的空白字符
        $psw = md5(trim($_POST["userpwd"]));  
        $psw_confirm = md5(trim($_POST["confirm"]));
        $code = $_POST["code"];
        if($user == "" || $psw == "" || $psw_confirm == "")  
        {  
            echo "<script>alert('请确认信息完整性！'); history.go(-1);</script>";  
        }
        else if($code != $_SESSION[' ver_code']){
            echo "<script>alert('验证码不正确，请重新输入！'); history.go(-1);</script>";
        }  
        else   
        {  
            if($psw == $psw_confirm)  
            {  
                $conn = mysqli_connect("localhost","root","root");   //连接数据库,帐号密码为自己数据库的帐号密码  
                if(mysqli_errno($conn)){
                    echo mysqli_error($conn);
                    exit;
                }
                mysqli_select_db($conn,"userdb");  //选择数据库  
                mysqli_set_charset($conn,'utf8'); //设定字符集  
                $sql = "select username from user where username = '$user'"; //SQL语句
                $result = mysqli_query($conn,$sql);    //执行SQL语句  
                $num = mysqli_num_rows($result); //统计执行结果影响的行数  
                
                if($num)    //如果已经存在该用户  
                {  
                    echo "<script>alert('用户名已存在'); history.go(-1);</script>";  
                }  
                else    //不存在当前注册用户名称  
                {   
                    $ip=ip2long($_SERVER['REMOTE_ADDR']); // 把ip地址转换成整型
                    $time=time();
                    $sql_insert = "insert into `user` (`username`,`userpwd`,`createtime`,`createip`) values('" . $user . "','" . $psw ."','".$time."','".$ip."')";
                    $res_insert = mysqli_query($conn,$sql_insert);  
                    if($res_insert)  
                    {  
                        echo "<script>alert('注册成功！');window.location.href='login.php';</script>";  
                    }  
                    else  
                    {  
                        echo "<script>alert('系统繁忙，请稍候！'); history.go(-1);</script>";  
                    }  
                }  
            }  
            else  
            {  
                echo "<script>alert('密码不一致！'); history.go(-1);</script>";  
            }  
        }  
    }  
    else  
    {  
        echo "<script>alert('提交未成功！');</script>";  
    }  
?>

Answer 1

未注册这个变量?代码里木有看见