PHP function to achieve user login register

Php beginner to do some of the more common and useful page, click on the record slightly above
I used the bootstrap framework inside the modal box registered to do landing page, so the page more beautiful
results page:


successful registration conditions / features:
1) Users name can not conflict

2) must be the same password twice

3) user registration data added to the database
after 4) registration / login is successful, the user automatically logged

HTML code:

    <link rel="stylesheet" href="css/bootstrap.css">
    <li class="toggle"><a data-toggle="modal" href="#loginer">登录</a></li>
    <li class="toggle"><a data-toggle="modal" href="#register">注册</a></li>
    <li class="toggle hidden"><a id="nicheng" href="##"></a></li>
    <li class="toggle hidden"><a id="logout" href="##">注销</a></li>
//登录模态框
<div id="loginer" class="modal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel1"
     aria-hidden="true">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal">
                    <span aria-hidden="true">&times;</span><span class="sr-only">Close</span></button>
                <h4 class="modal-title">请登录</h4>
            </div>
            <form id="form_login" class="form-horizontal">
                <div class="modal-body">
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="zh1">用户名：</label>
                        <div class="col-sm-9 require">
                            <input type="text" class="form-control" name="username" id="zh1"
                                   pattern="\w{6,10}" required>
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="pw1">密码：</label>
                        <div class="col-sm-9 require">
                            <input type="password" pattern="\w{6,10}" class="form-control" name="pwd" id="pw1"
                                   required>
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="yzm">验证码：</label>
                        <div class="col-sm-5 require">
                            <input type="text" pattern="\d{4}" class="form-control" name="yzm" id="yzm"
                                   required>
                        </div>
                        <div class="col-sm-4">
                            <img src="php/idcode.php" alt="">
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label id="info" class="col-sm-4 control-label pull-left"></label>
                    </div>
                </div>
                <div class="modal-footer">
                    <button type="submit" class="btn btn-primary">登录</button>
                    <button type="button" class="btn btn-default" data-dismiss="modal">关闭</button>
                </div>
            </form>
        </div>
    </div>
</div>
//注册模态框
<div id="register" class="modal" tabindex="-1" role="dialog" aria-labelledby="myModalLabe2"
     aria-hidden="true">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal">
                    <span aria-hidden="true">&times;</span><span class="sr-only">Close</span></button>
                <h4 class="modal-title">请注册</h4>
            </div>
            <form id="form_regist" class="form-horizontal">
                <div class="modal-body">
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="zh2">用户名：</label>
                        <div class="col-sm-9 require">
                            <input type="text" class="form-control" name="username" id="zh2"
                                   pattern="\w{6,10}" required>
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="pw2">密码：</label>
                        <div class="col-sm-9 require">
                            <input type="password" pattern="\w{6,10}" class="form-control" name="pwd" id="pw2">
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="pw3">确认密码：</label>
                        <div class="col-sm-9 require">
                            <input type="password" pattern="\w{6,10}" class="form-control" name="repwd" id="pw3">
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label class="col-sm-3 control-label" for="lc">昵称：</label>
                        <div class="col-sm-9 require">
                            <input type="text" pattern="\S{2,10}" class="form-control" name="nc" id="lc">
                        </div>
                    </div>
                    <div class="form-group has-feedback">
                        <label id="wanner" class="col-sm-4 control-label pull-left"></label>
                    </div>
                </div>
                <div class="modal-footer">
                    <button type="submit" class="btn btn-primary">注册</button>
                    <button type="button" class="btn btn-default" data-dismiss="modal">关闭</button>
                </div>
            </form>
        </div>
    </div>
</div>

JS code:

<script src="js/jquery-2.1.3.js"></script>
<script src="js/bootstrap.min.js"></script>
<script>
    function toggle(){
        $.getJSON("php/get.php",function (res) {
            //获取当前用户是否登录
            if(res['flag']){//用户已经登录，显示昵称和注销选项
                $('li.toggle').toggleClass('hidden');
                $('#nicheng').html(res['nc'])
            }
        });
    }
    $('#form_login').submit(function (e) {/*登录*/
        e.preventDefault();/*阻止表单默认事件，页面全局刷新*/
        var data=$('#form_login').serialize();/*将表单里的数据包装起来*/
        $.getJSON('php/login.php',data,function (res) {
            /*data：将表单里的数据传给php，回调函数接受php返回来的值*/
            if(res==3){//用户名、密码、验证码都输入正确
                toggle();/*修改首页选项菜单*/
                $('#loginer').modal('hide');/*关闭模态框*/
            }else if(res==2){
                $('#info').html('用户名或密码有误')
            }else {
                $('#info').html('验证码有误')
            }
        })
    });
    $('#logout').click(function () {
        confirm('确定要注销？');
        $.getJSON('php/logout.php',function (res) {
            if(res)toggle();
        })
    })
    $('#form_regist').submit(function (e) {
        e.preventDefault();
        var data=$('#form_regist').serialize();
        $.getJSON('php/regist.php',data,function (res) {
            if(res==3){
                toggle();
                $('#register').modal('hide');
            }else if (res==2) {
                $('#wanner').html('两次密码不一致，请重试！')
            }else if (res==1) {
                $('#wanner').html('用户名冲突，请重试！')
            }
        })
    });

the connect.php (connection database):

<?php
$link=new PDO("mysql:host=localhost;port=3306;dbname=db","root","");
$link->query("set names utf8");

get.php (judgment logged in): the unregistered login registration options, switch the display to the user login and logout option nickname

<?php
include_once ("connect.php");
session_start();/*开启会话*/
if (isset($_SESSION['username'])){
   /* 判断用户会话里用户名是否存在，即用户是否登录*/
    $json['nc']=$_SESSION['nc'];/*把昵称存起来，一会返回给首页*/
    $json['flag']=true;/*用户已经登录，标志flag为true*/
}else
    $json['flag']=false;/*用户已经登录，标志flag为true*/
echo json_encode($json);/*返回json*/

regist.php (Registered): The value of the flag FLAG is determined in three states registered

<?php
include_once ("connect.php");
$user=$_GET['username'];//获取表单提交的数据
$pwd=$_GET['pwd'];
$repwd=$_GET['repwd'];
$nc=$_GET['nc'];
$row=$link->query("select * from `user` where username='$user'");
/*查询数据库中是否存在用户名相同的用户*/
if ($row->rowCount()){
    $flag=1;/*存在用户名相同，即用户名冲突*/
}else if ($pwd!=$repwd){
   $flag=2;/*两次密码不相同*/
}else{/*插入数据进数据库*/
    $row=$link->exec("insert into`user`( `username`,  `pwd`，`nc`) values ('$user','$pwd','$nc')");
    session_start();/*打开会话，将用户名和昵称存起来*/
    $_SESSION['username']=$user;
    $_SESSION['nc']=$nc;
    $flag=3;/*注册成功标志*/
}
echo $flag;

login.php (Login): what went wrong according to the success or login operation judgment flag flag

<?php
include_once ("connect.php");
session_start();/*开启会话*/
$user=$_GET['username'];/*获取登录表单提交过来的数据*/
$pwd=$_GET['pwd'];
$yzm=$_GET['yzm'];
if($yzm==$_SESSION['vCode']){/*当用户输入的验证码和图片验证码相同时*/
    $result=$link->query("select * from `user` where username='$user' and pwd='$pwd'");
    $link = null;
    $row = $result->fetch();/*读取从数据库获取的数据*/
    if ($row) {/*如果数据存在，即用户登录成功*/
        $_SESSION['username'] = $row['username'];
        /*将用户名和昵称存在服务器，可以多个页面使用*/
        $_SESSION['nc'] = $row['nc'];
        $flag=3;
    }else{/*用户名或密码错误*/
        $flag=2;
    }
}else{/*验证码输入错误*/
    $flag=1;
}
echo $flag;

logout.php (log off): direct destruction of session variables, then get.php not get inside nc ie username and determines whether the user has logged out

<?php
session_start();
unset($_SESSION['username']);//销毁用户名
unset($_SESSION['nc']);//销毁昵称
echo json_encode(true);//返回结果

CAPTCHA code automatically generated login page, in an article in my other
https://www.cnblogs.com/xyyl/p/10901100.html