基于PHP的登录和注册的功能的实现

<div class="sign-con w1200">
			<img src="img/logn-tu.gif" class="sign-contu f-l"/>
			<form action="login.php" method="post">
				<div class="sign-ipt f-l">
					<p>用户名：</p>
					<input type="text" name="username" placeholder="手机号/邮箱" />
					<p>密码：</p>
					<input type="password" name="password" placeholder="密码可见" />
					<br />
					<button class="slig-btn">登录</button>
					<p>
						没有账号？请
						<a href="regist.html" rel="external nofollow" >注册</a>
						<a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="wj">忘记密码？</a>
					</p>
					<div class="sign-qx">
						<a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="f-r">
							<img src="img/sign-xinlan.gif" />
						</a>
						<a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="qq f-r">
							<img src="img/sign-qq.gif" />
						</a>
						<div style="clear: both;"></div>
					</div>
				</div>
			</form>
			<div style="clear: both;"></div>
		</div>

<div class="password-con registered">
			<form action="regist.php" method="post">
				<div class="psw">
					<p class="psw-p1">用户名</p>
					<input type="text" name="username" placeholder="HR了" />
					<span class="dui"></span>
				</div>
				<div class="psw">
					<p class="psw-p1">输入密码</p>
					<input type="password" name="password" placeholder="请输入密码" />
					<span class="cuo">密码由6-16的字母、数字、符号组成</span>
				</div>
				<div class="psw">
					<p class="psw-p1">确认密码</p>
					<input type="password" name="repassword" placeholder="请再次输入密码" />
					<span class="cuo">密码不一致，请重新输入</span>
				</div>
				<div class="psw psw2">
					<p class="psw-p1">手机号/邮箱</p>
					<input type="text" name="telphone" placeholder="请输入手机/邮箱验证码" />
					<button>获取短信验证码</button>
				</div>
				<div class="psw psw3">
					<p class="psw-p1">验证码</p>
					<input type="text" placeholder="请输入验证码" />
				</div>
				<div class="yanzhentu">
					<div class="yz-tu f-l">
						<img src="img/psw-yanzhengtu.gif" />
					</div>
					<p class="f-l">
						看不清楚？
						<a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >换张图</a>
					</p>
					<div style="clear: both;"></div>
				</div>
				<div class="agreement">
					<input type="checkbox" name="hobby" />
					<p>
						我有阅读并同意
						<span>《宅客微购网站服务协议》</span>
					</p>
				</div>
				<button type="submit" value="注册" class="psw-btn">立即注册</button>
				<p class="sign-in">
					已有账号？请
					<a href="login.html" rel="external nofollow" >登录</a>
				</p>
			</form>
		</div><!-- 注册框结束 -->

<?php
  header("Content-type: text/html; charset=utf-8");
  $username = $_POST['username'];
  $password = $_POST['password'];
  $conn = new mysqli('localhost','root','root','shopping');
  if ($conn->connect_error){
    echo '数据库连接失败！';
    exit(0);
  }else{
    if ($username == ''){
      echo '<script>alert("请输入用户名！");history.go(-1);</script>';
      exit(0);
    }
    if ($password == ''){
      echo '<script>alert("请输入密码！");history.go(-1);</script>';
      exit(0);
    }
    $sql = "select username,password from userinfo where username = '$_POST[username]' and password = '$_POST[password]'";
    $result = $conn->query($sql);
    $number = mysqli_num_rows($result);
    if ($number) {
      echo '<script>window.location="index.html";</script>';
    } else {
      echo '<script>alert("用户名或密码错误！");history.go(-1);</script>';
    }
  }
?>

<?php
  header("Content-type: text/html; charset=utf-8");
    $username = $_POST['username'];
    $password = $_POST['password'];
    $repassword = $_POST['repassword'];
    $telphone = $_POST['telphone'];
    if ($username == ''){
      echo '<script>alert("请输入用户名！");history.go(-1);</script>';
      exit(0);
    }
    if ($password == ''){
      echo '<script>alert("请输入密码");history.go(-1);</script>';
      exit(0);
    }
    if ($password != $repassword){
      echo '<script>alert("密码与确认密码应该一致");history.go(-1);</script>';
      exit(0);
    }
    if($password == $repassword){
      $conn = new mysqli('localhost','root','root','shopping');
      if ($conn->connect_error){
        echo '数据库连接失败！';
        exit(0);
      }else {
        $sql = "select username from userinfo where username = '$_POST[username]'";
        $result = $conn->query($sql);
        $number = mysqli_num_rows($result);
        if ($number) {
          echo '<script>alert("用户名已经存在");history.go(-1);</script>';
        } else {
          $sql_insert = "insert into userinfo (username,password,telphone) values('$_POST[username]','$_POST[password]','$_POST[telphone]')";
          $res_insert = $conn->query($sql_insert);
          if ($res_insert) {
            echo '<script>window.location="index.html";</script>';
          } else {
            echo "<script>alert('系统繁忙，请稍候！');</script>";
          }
        }
      }
    }else{
      echo "<script>alert('提交未成功！'); history.go(-1);</script>";
    }
?>