以下是一个简单的 PHP 注册登录代码示例，包括前端和后端代码：
前端代码：
```
<html>
<head>
<title>PHP Registration/Login System</title>
</head>
<body>
<h2>Register</h2>
<form method="post" action="register.php">
<label>Username:</label>
<input type="text" name="username" required><br>
<label>Password:</label>
<input type="password" name="password" required><br>
<input type="submit" value="Register">
</form>
<h2>Login</h2>
<form method="post" action="login.php">
<label>Username:</label>
<input type="text" name="username" required><br>
<label>Password:</label>
<input type="password" name="password" required><br>
<input type="submit" value="Login">
</form>
</body>
</html>
```
后端代码：
register.php
```
<?php
// Connect to database
$conn = mysqli_connect("localhost", "username", "password", "database");
// Check connection
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
// Get form data
$username = $_POST['username'];
$password = $_POST['password'];
// Check if username already exists
$query = "SELECT * FROM users WHERE username='$username'";
$result = mysqli_query($conn, $query);
if (mysqli_num_rows($result) > 0) {
echo "Username already exists";
} else {
// Insert new user to database
$query = "INSERT INTO users (username, password) VALUES ('$username', '$password')";
mysqli_query($conn, $query);
echo "Registration successful";
}
// Close database connection
mysqli_close($conn);
?>
```
login.php
```
<?php
// Connect to database
$conn = mysqli_connect("localhost", "username", "password", "database");
// Check connection
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
// Get form data
$username = $_POST['username'];
$password = $_POST['password'];
// Check if username and password are correct
$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($conn, $query);
if (mysqli_num_rows($result) > 0) {
echo "Login successful";
} else {
echo "Invalid username or password";
}
// Close database connection
mysqli_close($conn);
?>
```
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