PHP入门指南：从基础开始

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

$my_var = "Hello, world!";
echo $my_var;

$my_integer = 10;
$my_float = 1.5;
$my_string = "Hello, world!";
$my_array = array("John", "Peter", "Lisa");

var_dump($my_integer);
var_dump($my_float);
var_dump($my_string);
var_dump($my_array);

int(10)
float(1.5)
string(13) "Hello, world!"
array(3) {
  [0]=>
  string(4) "John"
  [1]=>
  string(5) "Peter"
  [2]=>
  string(4) "Lisa"
}

$num = 7;

if ($num > 10) {
  echo "The number is greater than 10";
} else if ($num > 5) {
  echo "The number is greater than 5 but less than or equal to 10";
} else {
  echo "The number is less than or equal to 5";
}

$i = 1;

while ($i < 10) {
  echo $i . " ";
  $i++;
}

function add_numbers($num1, $num2) {
  return $num1 + $num2;
}

echo add_numbers(3, 5);

$server = "localhost";
$username = "root";
$password = "";
$dbname = "mydatabase";

$conn = new PDO("mysql:host=$server;dbname=$dbname", $username, $password);

$sql = "SELECT * FROM users";
$stmt = $conn->prepare($sql);
$stmt->execute();

$results = $stmt->fetchAll();