用代码实现一个考试系统，具体要求如下1.该在线考试系统 需安装Web服务器，本实验推荐使用 phpstudy 软件进行开发2.该考试系统至少需要具有 5 题以上的单项选择题，每一题具有四个备选项，总分为100分3. 需要使用数据库系统存放用户的用户名和密码、题库及题目、学生的答题记录、学生每题的得分、学生的总成绩、学生的测试次数及每一次测试的详细信息，需要有学生的身份确认功能，只有登录成功的学生才能开始答题并记录学生的测试成绩4.该系统能够对用户的答题进行自动评分（因为是单项选择题，有标准答案），总分为100分 5.需要使用 数据库 存放题目和学生的答题情况，推荐使用 mysql 数据库。

好的，以下是一个简单的 PHP 实现考试系统的示例代码：

1. 数据库连接与创建

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 创建用户表
$sql = "CREATE TABLE users (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(30) NOT NULL,
password VARCHAR(30) NOT NULL
)";
if (mysqli_query($conn, $sql)) {
    echo "Table users created successfully";
} else {
    echo "Error creating table: " . mysqli_error($conn);
}

// 创建题目表
$sql = "CREATE TABLE questions (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
question TEXT NOT NULL,
option_a TEXT NOT NULL,
option_b TEXT NOT NULL,
option_c TEXT NOT NULL,
option_d TEXT NOT NULL,
answer CHAR(1) NOT NULL
)";
if (mysqli_query($conn, $sql)) {
    echo "Table questions created successfully";
} else {
    echo "Error creating table: " . mysqli_error($conn);
}

// 关闭数据库连接
mysqli_close($conn);
?>

2. 用户注册

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 处理用户提交的注册信息
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    $password = $_POST["password"];

    // 将用户名和密码插入用户表
    $sql = "INSERT INTO users (username, password) VALUES ('$username', '$password')";
    if (mysqli_query($conn, $sql)) {
        echo "User registered successfully";
    } else {
        echo "Error registering user: " . mysqli_error($conn);
    }
}

// 关闭数据库连接
mysqli_close($conn);
?>

3. 用户登录

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 处理用户提交的登录信息
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    $password = $_POST["password"];

    // 在用户表中查找匹配的用户名和密码
    $sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
    $result = mysqli_query($conn, $sql);

    // 如果找到了匹配的用户，则登陆成功
    if (mysqli_num_rows($result) == 1) {
        echo "Login success";
    } else {
        echo "Invalid username or password";
    }
}

// 关闭数据库连接
mysqli_close($conn);
?>

4. 显示题目和答案

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 从题目表中随机选择 5 道题目并显示在页面上
$sql = "SELECT * FROM questions ORDER BY RAND() LIMIT 5";
$result = mysqli_query($conn, $sql);

while ($row = mysqli_fetch_assoc($result)) {
    echo "<p>" . $row["question"] . "</p>";
    echo "<ul>";
    echo "<li><input type='radio' name='" . $row["id"] . "' value='A'>" . $row["option_a"] . "</li>";
    echo "<li><input type='radio' name='" . $row["id"] . "' value='B'>" . $row["option_b"] . "</li>";
    echo "<li><input type='radio' name='" . $row["id"] . "' value='C'>" . $row["option_c"] . "</li>";
    echo "<li><input type='radio' name='" . $row["id"] . "' value='D'>" . $row["option_d"] . "</li>";
    echo "</ul>";
}

// 关闭数据库连接
mysqli_close($conn);
?>

5. 自动评分

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 处理用户提交的答案，并计算得分
$score = 0;
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    foreach ($_POST as $question_id => $answer) {
        // 在题目表中查找该题目的正确答案
        $sql = "SELECT * FROM questions WHERE id=$question_id";
        $result = mysqli_query($conn, $sql);
        $row = mysqli_fetch_assoc($result);

        // 如果用户选择的答案与正确答案相同，则加分
        if ($answer == $row["answer"]) {
            $score += 20;
        }
    }

    // 显示得分
    echo "Score: " . $score;

    // 将学生的答题记录插入记录表
    $sql = "INSERT INTO records (student_id, score) VALUES (1, $score)";
    if (mysqli_query($conn, $sql)) {
        echo "Record inserted successfully";
    } else {
        echo "Error inserting record: " . mysqli_error($conn);
    }
}

// 关闭数据库连接
mysqli_close($conn);
?>

6. 显示学生的测试成绩和测试次数

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "exam_system";

$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// 获取学生的测试次数和总成绩
$sql = "SELECT COUNT(*) AS count, SUM(score) AS total_score FROM records WHERE student_id=1";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_assoc($result);

// 显示学生的测试次数和总成绩
echo "Test count: " . $row["count"] . "<br>";
echo "Total score: " . $row["total_score"];

// 关闭数据库连接
mysqli_close($conn);
?>

以上是一个简单的 PHP 实现考试系统的示例代码，具体实现时还需要根据实际情况进行调整和完善。