PHP if Statements
PHP if Statements and Secure Login Example
Introduction:
Explore the fundamentals of PHP if statements and their application in building a secure login system. This lesson provides hands-on examples and best practices for conditional statements in PHP, along with a practical demonstration of creating a login page. Gain insights into user authentication, form handling, and enhancing security in PHP web development.
In PHP, if statements are used to conditionally execute code based on whether a specified condition evaluates to true or false.
The basic syntax of an if statement looks like this:
if (condition) {
// code to be executed if the condition is true
}
Here’s a simple example:
<?php
$number = 10;
if ($number > 5) {
echo "The number is greater than 5.";
}
?>
In this example, the condition is $number > 5. If the value of $number is indeed greater than 5, the code inside the curly braces will be executed, and the message “The number is greater than 5.” will be printed.
You can also use an else statement to specify code that should be executed when the condition is false:
<?php
$number = 3;
if ($number > 5) {
echo "The number is greater than 5.";
} else {
echo "The number is not greater than 5.";
}
?>
In this case, since $number is not greater than 5, the code inside the else block will be executed, and the message “The number is not greater than 5.” will be printed.
You can also use elseif to check multiple conditions:
<?php
$number = 5;
if ($number > 5) {
echo "The number is greater than 5.";
} elseif ($number < 5) {
echo "The number is less than 5.";
} else {
echo "The number is equal to 5.";
}
?>
Here, the script checks if $number is greater than 5, less than 5, or equal to 5, and prints the corresponding message accordingly.
Remember to replace “condition” with the actual expression you want to evaluate in your if statement. The code inside the curly braces will be executed only if the condition is true.
complete example in html with explanation
Below is a complete example of a simple HTML page with embedded PHP code using if statements.
This example demonstrates a basic login form that checks the entered credentials:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Login Page</title>
</head>
<body>
<?php
// Sample user credentials
$correctUsername = 'user123';
$correctPassword = 'pass123';
// Check if the form is submitted
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
// Retrieve user input from the form
$enteredUsername = $_POST['username'];
$enteredPassword = $_POST['password'];
// Check if the entered credentials match the correct ones
if ($enteredUsername === $correctUsername && $enteredPassword === $correctPassword) {
$message = "Login successful!";
} else {
$message = "Invalid username or password. Please try again.";
}
}
?>
<h2>Login Form</h2>
<?php
// Display the login result message, if available
if (isset($message)) {
echo "<p>$message</p>";
}
?>
<form method="post" action="">
<label for="username">Username:</label>
<input type="text" id="username" name="username" required><br>
<label for="password">Password:</label>
<input type="password" id="password" name="password" required><br>
<button type="submit">Login</button>
</form>
</body>
</html>
Explanation:
- HTML Structure: The HTML structure is a basic login form within the <body> tag. It includes a form with fields for entering a username and password.
- PHP Code Block: The PHP code block at the top of the file checks whether the form has been submitted ($_SERVER[‘REQUEST_METHOD’] === ‘POST’). If submitted, it retrieves the entered username and password from the $_POST superglobal.
- Conditional Statements: Inside the PHP block, there’s an if statement checking if the entered credentials match the correct ones. Based on the result, it sets a message to be displayed later.
- HTML/PHP Integration: The login result message is displayed below the form using another PHP block. It checks if the $message variable is set and echoes the appropriate message.
- Form Submission: The form has the method=”post” attribute, and it sends the form data to the same page (empty action=”” means it submits to the current URL).
This example demonstrates how PHP if statements can be used in the context of an HTML page, especially for handling form submissions and displaying messages based on conditions.
An application login page and a dashboard page
Let’s create a simple PHP application that simulates user authentication. This application will have a login page and a dashboard page. The login credentials are hardcoded for simplicity.
File Structure:
index.php: The main login page.
dashboard.php: The dashboard page to be displayed upon successful login.
index.php:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Login Page</title>
</head>
<body>
<?php
// Sample user credentials
$correctUsername = 'user123';
$correctPassword = 'pass123';
// Check if the form is submitted
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
// Retrieve user input from the form
$enteredUsername = $_POST['username'];
$enteredPassword = $_POST['password'];
// Check if the entered credentials match the correct ones
if ($enteredUsername === $correctUsername && $enteredPassword === $correctPassword) {
// Redirect to the dashboard upon successful login
header('Location: dashboard.php');
exit();
} else {
$message = "Invalid username or password. Please try again.";
}
}
?>
<h2>Login Form</h2>
<?php
// Display the login result message, if available
if (isset($message)) {
echo "<p style='color: red;'>$message</p>";
}
?>
<form method="post" action="">
<label for="username">Username:</label>
<input type="text" id="username" name="username" required><br>
<label for="password">Password:</label>
<input type="password" id="password" name="password" required><br>
<button type="submit">Login</button>
</form>
</body>
</html>
dashboard.php:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Dashboard</title> </head> <body> <h2>Welcome to the Dashboard!</h2> <p>This is a secure area accessible only to authenticated users.</p> <a href="index.php">Logout</a> </body> </html>
In this example:
- index.php is the main login page.
- dashboard.php is the dashboard page that should only be accessible after a successful login.
- When a user enters the correct credentials on the login page, they are redirected to the dashboard.
- The “Logout” link on the dashboard links back to the login page.
- Note that this is a simple example for educational purposes, and in a real-world scenario, you would likely use a database for storing user credentials and employ more secure authentication mechanisms.
Here’s a single web page containing both the login page and the dashboard. Copy and paste the code into a single PHP file (e.g., index.php):
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Login Page</title>
</head>
<body>
<?php
// Sample user credentials
$correctUsername = 'user123';
$correctPassword = 'pass123';
// Check if the form is submitted
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
// Retrieve user input from the form
$enteredUsername = $_POST['username'];
$enteredPassword = $_POST['password'];
// Check if the entered credentials match the correct ones
if ($enteredUsername === $correctUsername && $enteredPassword === $correctPassword) {
// Redirect to the dashboard upon successful login
header('Location: index.php?page=dashboard');
exit();
} else {
$message = "Invalid username or password. Please try again.";
}
}
?>
<?php if (!isset($_GET['page']) || $_GET['page'] !== 'dashboard') { ?>
<h2>Login Form</h2>
<?php
// Display the login result message, if available
if (isset($message)) {
echo "<p style='color: red;'>$message</p>";
}
?>
<form method="post" action="">
<label for="username">Username:</label>
<input type="text" id="username" name="username" required><br>
<label for="password">Password:</label>
<input type="password" id="password" name="password" required><br>
<button type="submit">Login</button>
</form>
<?php } else { ?>
<h2>Welcome to the Dashboard!</h2>
<p>This is a secure area accessible only to authenticated users.</p>
<a href="index.php">Logout</a>
<?php } ?>
</body>
</html>
This single PHP file includes both the login form and the dashboard content. The $_GET[‘page’] variable is used to determine whether to display the login form or the dashboard content. The header(‘Location: index.php?page=dashboard’) line redirects the user to the dashboard upon successful login. The “Logout” link on the dashboard links back to the login form.
Explanation
Let’s go through the code and provide an explanation for each part:
HTML Structure:
The document starts with the usual HTML structure, including the <!DOCTYPE html> declaration, the <html>, <head>, and <body> tags.
PHP Code Block for Authentication:
- Sample user credentials ($correctUsername and $correctPassword) are defined.
- These are hardcoded for simplicity; in a real-world scenario, you would use a more secure authentication system.
- The PHP code block checks if the form has been submitted ($_SERVER[‘REQUEST_METHOD’] === ‘POST’).
- If submitted, it retrieves the entered username and password from the $_POST superglobal.
- It checks if the entered credentials match the correct ones. If so, it redirects the user to the dashboard using header(‘Location: index.php?page=dashboard’) and exits the script.
Conditional Display of Login Form and Dashboard:
- The code uses <?php if (!isset($_GET[‘page’]) || $_GET[‘page’] !== ‘dashboard’) { ?> to check if the page parameter is not set or is not equal to ‘dashboard’. If true, it displays the login form.
- Inside this block, it checks if there is a login result message ($message) and displays it in red if present.
- The login form includes fields for entering a username and password, and a submit button.
- The code uses <?php } else { ?> to handle the case when the page parameter is set to ‘dashboard’. In this case, it displays the dashboard content.
- The dashboard content includes a welcome message and a “Logout” link that points back to the login form.
This single PHP file acts as both the login page and the dashboard. It dynamically switches between displaying the login form and the dashboard content based on the presence of the page parameter in the URL. The redirection to the dashboard after a successful login is done using the header(‘Location: index.php?page=dashboard’) statement.
Quiz bout PHP if statements
Here’s a quiz with 15 questions related to PHP if statements and the login page example.
Quiz: PHP if Statements and Login Page
1-What is the primary purpose of an if statement in PHP?
A. Looping
B. Conditional execution
C. Defining functions
D. Variable declaration
2-In PHP, what does the $_SERVER[‘REQUEST_METHOD’] variable check?
A. Current date and time
B. Server software version
C. Request method (e.g., GET or POST)
D. User agent information
3-How can you prevent SQL injection in a real-world login system?
A. Use $_REQUEST for form data
B. Hardcode all user credentials
C. Validate and sanitize user input
D. Display raw error messages
4-What does the header(‘Location: index.php’) function do in PHP?
A. Prints a header message
B. Redirects the user to another page
C. Sets a cookie
D. Includes an external file
5-In PHP, how can you check if a variable is set and not empty?
A. isset()
B. empty()
C. isset() && !empty()
D. Both A and B
5-What is the purpose of the exit(); statement in PHP?
A. Terminates the PHP script
B. Echoes a message to the user
C. Redirects the user
D. Creates an infinite loop
6-How would you check multiple conditions using if, elseif, and else in PHP?
A. Using switch statement
B. Using nested if statements
C. Using only if statements
D. Using if, elseif, and else statements
7-What is the purpose of the <!DOCTYPE html> declaration in an HTML document?
A. Specifies the HTML version
B. Declares the document as an HTML5 document
C. Defines the character set
D. Comments out HTML code
8-How do you retrieve user input from a form in PHP?
A. $form->input()
B. $_GET[‘input’]
C. $_POST[‘input’]
D. Both B and C
9-In the login example, what is the purpose of $correctUsername and $correctPassword?
A. To display error messages
B. To check if the form is submitted
C. To simulate correct user credentials
D. To set the title of the HTML page
10-Which PHP function is used to output text or HTML to the browser?
A. echo
B. print
C. display
D. output
11-What does the required attribute do in an HTML form input field?
A. Specifies the field as mandatory
B. Limits the input length
C. Validates the input format
D. Disables the input field
12-How can you safely handle user authentication in a real-world scenario?
A. Store passwords in plain text
B. Use a secure hash algorithm for passwords
C. Email passwords to users
D. Display detailed login error messages
13-What is the purpose of the method=”post” attribute in an HTML form?
A. Specifies the form’s action URL
B. Sets the form’s encoding type
C. Defines the HTTP method for form submission
D. Disables form submission
14-In the login example, what is the purpose of header(‘Location: index.php?page=dashboard’)?
A. Includes an external file
B. Redirects the user to the dashboard page
C. Sets a cookie
D. Outputs a header message
Answers:
B, 2. C, 3. C, 4. B, 5. C, 6. A, 7. D, 8. B, 9. D, 10. C, 11. A, 12. A, 13. B, 14. C, 15. B