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深入了解PHP：從入門到精通

引言：
PHP是一種廣泛應用于web開發的服務器端腳本語言，它簡單易學，適用于初學者，也提供了豐富的功能和擴展性，能夠滿足復雜的開發需求。本文將從入門到精通，通過具體的代碼示例，帶您逐步了解PHP的各個方面。

一、基礎知識

變量聲明和輸出

$name = "John";
$age = 25;
echo "My name is " . $name . " and I am " . $age . " years old.";

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條件語句

$score = 90;
if ($score >= 60) {
 echo "You passed the exam!";
} else {
 echo "You failed the exam.";
}

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循環語句

for ($i = 0; $i < 5; $i++) {
 echo $i;
}

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函數的定義和調用

function sayHello($name) {
 echo "Hello, " . $name . "!";
}
sayHello("Tom");

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二、數組和字符串

數組的聲明和遍歷

$fruits = ["apple", "banana", "orange"];
foreach ($fruits as $fruit) {
 echo $fruit;
}

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字符串操作

$str = "Hello, PHP!";
echo strlen($str);  // 輸出：12
echo strtoupper($str);  // 輸出：HELLO, PHP!
echo substr($str, 7);  // 輸出：PHP!

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三、數據庫操作

連接數據庫

$servername = "localhost";
$username = "root";
$password = "123456";
$dbname = "myDB";
$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
 die("Connection failed: " . mysqli_connect_error());
}

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查詢數據

$sql = "SELECT * FROM users";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
 while ($row = mysqli_fetch_assoc($result)) {
     echo "Name: " . $row['name'] . ", Age: " . $row['age'];
 }
} else {
 echo "No results found.";
}

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插入數據

$sql = "INSERT INTO users (name, age) VALUES ('John', 25)";
if (mysqli_query($conn, $sql)) {
 echo "Data inserted successfully.";
} else {
 echo "Error: " . mysqli_error($conn);
}

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四、面向對象編程

類的定義和實例化

class Car {
 public $color;
 public function drive() {
     echo "Driving...";
 }
}
$car = new Car();
$car->color = "red";
$car->drive();

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繼承和多態

class SportsCar extends Car {
 public function drive() {
     echo "Driving at high speed!";
 }
}
$sportsCar = new SportsCar();
$sportsCar->color = "blue";
$sportsCar->drive();

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五、常見應用

文件上傳

<form action="upload.php" method="POST" enctype="multipart/form-data">
 <input type="file" name="file">
 <input type="submit" value="Upload">
</form>

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$targetDir = "uploads/";
$targetFile = $targetDir . basename($_FILES["file"]["name"]);
if (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
 echo "File uploaded successfully.";
} else {
 echo "Error uploading file.";
}

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用戶注冊與登錄

$hashedPassword = password_hash($password, PASSWORD_DEFAULT);
$sql = "INSERT INTO users (username, password) VALUES ('$username', '$hashedPassword')";
if (mysqli_query($conn, $sql)) {
 echo "Registration successful. You can now login.";
} else {
 echo "Error: " . mysqli_error($conn);
}

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$sql = "SELECT * FROM users WHERE username = '$username'";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
 $row = mysqli_fetch_assoc($result);
 if (password_verify($password, $row['password'])) {
     echo "Login successful.";
 } else {
     echo "Password incorrect.";
 }
} else {
 echo "Username not found.";
}

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結語：
通過本文的介紹和實例代碼，希望讀者能夠從PHP的基礎知識開始，逐步深入了解PHP的各個方面，從而掌握PHP的高級應用技巧，提升自己的開發能力。同時，也歡迎讀者在實踐中探索更多有趣和創新的PHP應用。