🎓 PHP 开发教程

<?php
echo "Hello, World!";
?>

<?php
  // PHP代码
?>

<?php
// 单行注释

# 另一种单行注释

/*
  多行
  注释
*/
?>

<?php
$name = "John";      // 字符串变量
$age = 30;           // 整型变量
$height = 1.85;      // 浮点型变量
$isStudent = true;   // 布尔型变量
?>

<?php
define("SITE_NAME", "我的网站");
define("MAX_USERS", 100);
?>

<?php
$a = 10;
$b = 3;

echo $a + $b;  // 13 (加法)
echo $a - $b;  // 7  (减法)
echo $a * $b;  // 30 (乘法)
echo $a / $b;  // 3.333... (除法)
echo $a % $b;  // 1  (取余)
?>

<?php
$a = 5;
$b = "5";

$a == $b   //  (值相等)
$a === $b // (值和类型都相等)
$a != $b  // (值不等)
$a !== $b // (值和类型都不相等)
?>

<?php
$score = 85;

if ($score >= 90) {
    echo "优秀";
} elseif ($score >= 80) {
    echo "良好";  // 输出此项
} else {
    echo "继续努力";
}
?>

<?php
for ($i = 0; $i < 5; $i++) {
    echo "迭代 #$i<br>";
}
?>

<?php
$count = 3;
while ($count > 0) {
    echo "倒计时: $count<br>";
    $count--;
}
?>

<?php
function greet($name) {
    return "你好, $name!";
}

echo greet("康浩焜"); // 输出: 你好, 康浩焜!
?>

<?php
function sayHello($name = "徐柏伦") {
    return "你好, $name!";
}

echo sayHello();      // 输出: 你好, 徐柏伦!
echo sayHello("王煜衡"); // 输出: 你好, 王煜衡!
?>

<?php
$fruits = ["苹果", "香蕉", "橙子"];
echo $fruits[1]; // 输出: 香蕉
?>

<?php
$person = [
    "name" => "嵇欣璇",
    "age" => 19,
    "email" => "jixinxuan@example.com"
];

echo $person["email"]; // 输出: jixinxuan@example.com
?>

<?php
$colors = ["红", "绿", "蓝"];

foreach ($colors as $color) {
    echo "$color ";
}
// 输出: 红 绿 蓝
?>

<?php
session_start(); // 开启 Session，放在页面最前面

            // 设置 Session 变量
            $_SESSION['user'] = 'admin';
            $_SESSION['password'] = '123456';

            // 读取 Session 变量
            echo $_SESSION['user']; // 输出：admin

            // 销毁 Session 变量
            unset($_SESSION['user']);

            // 关闭 Session
            session_destroy();
?>

<?php  
// 连接 MySQL 数据库    
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}

// 关闭 mysqli 连接    
$conn->close();
?>  

<?php  
……
$sql = "SELECT `id`, `firstname`, `lastname` FROM `MyGuests`";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 结果";
}

// 关闭 mysqli 连接
$conn->close();
?>  

<?php  
……
$sql = "INSERT INTO `MyGuests` (`firstname`, `lastname`, `email`)
VALUES ('John', 'Doe', 'john@example.com')";
$result = $conn->query($sql);

// 关闭 mysqli 连接
$conn->close();
?>  

<?php  
……
$sql="UPDATE `Persons` SET Age=36
WHERE FirstName='Peter' AND LastName='Griffin'";
$result = $conn->query($sql);

// 关闭 mysqli 连接
mysqli_close($con);
?>  

<?php  
……
$sql="DELETE FROM `Persons` WHERE `LastName` ='Griffin'";
$result = $conn->query($sql);

// 关闭 mysqli 连接
mysqli_close($con);
?>  

$stmt = $conn->prepare("INSERT INTO `MyGuests` (firstname, lastname, email) VALUES (?, ?, ?)");
$stmt->bind_param("sss", $firstname, $lastname, $email);

<?php
$data = array(
    "name" => "张三",
    "age" => 25,
    "city" => "北京",
    "hobbies" => array("阅读", "游泳", "编程")
);

$json_string = json_encode($data, JSON_UNESCAPED_UNICODE);
echo $json_string;
?>

<?php
$json_string = '{"name":"王五","age":28,"city":"上海"}';

// 转换为关联数组
$array = json_decode($json_string, true);
echo $array["name"]; // 输出：王五

// 转换为对象
$object = json_decode($json_string);
echo $object->name; // 输出：王五
?>