Definition and function introduction of PHP

Definition and function introduction of PHP

PHP is a server-side scripting language, originally developed in 1994 by Rasmus Lerdorf. Its initials originally meant "Personal Home Page" and are now interpreted as "Hypertext Preprocessor". This language is mainly used in the field of web development. PHP is used in conjunction with HTML to create dynamic pages, process form data, connect to databases and other functions. The following will introduce some basic functions of PHP and provide specific code examples.

1. Variables and data types
   Variables in PHP start with the $ symbol, and there is no need to declare the data type in advance. PHP supports various data types, including integers, floating point numbers, strings, Boolean values, arrays, etc.

Example:

<?php
$name = "Alice";
$age = 25;
$height = 1.65;
$isStudent = true;
$fruits = array("apple", "banana", "orange");
?>

2. Control flow
   PHP supports common control flow structures, such as if statements, for loops, while loops, etc.

Example:

<?php
$grade = 85;

if ($grade >= 60) {
    echo "及格";
} else {
    echo "不及格";
}

for ($i = 1; $i <= 5; $i++) {
    echo $i . " ";
}

$num = 0;
while ($num < 3) {
    echo $num . " ";
    $num++;
}
?>

3. Function
   PHP allows defining and calling functions, which can accept parameters and return values.

Example:

<?php
function add($a, $b) {
    return $a + $b;
}

echo add(3, 5); // 输出8
?>

4. Database connection
   PHP can connect to various databases, the most common one is MySQL. Through database connection, operations such as data query, insertion, update, and deletion can be performed.

Example:

<?php
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "myDB";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 查询数据库
$sql = "SELECT id, name, age FROM students";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"]. " - Name: " . $row["name"]. " - Age: " . $row["age"]. "<br>";
    }
} else {
    echo "0 结果";
}

$conn->close();
?>

The above is an introduction to some basic functions of PHP. As a powerful server-side scripting language, PHP is widely used in Web development. Hope the above content is helpful to you.

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