PHP First Page, Comments

You are advised to check corresponding YouTube video at the end of this article.

In PHP, the <?php and ?> tags are used to enclose PHP code in a file. These tags tell the web server that the enclosed code should be processed as PHP code, and not as plain text or HTML.

When the web server encounters the <?php tag, it starts interpreting and executing the PHP code until it reaches the ?> tag. Anything outside of the PHP tags is treated as plain text or HTML and is sent directly to the browser without any processing by the PHP engine.

The reason why we need to use the <?php and ?> tags when writing PHP code is to separate the PHP code from the rest of the content on the web page. This separation allows us to create dynamic web pages that include HTML, CSS, and JavaScript along with the PHP code.

It is important to note that in modern PHP development, the <?php tag is often omitted, and the code is enclosed in short tags <? and ?> or the echo tag <?=, which can make the code more concise and readable. However, this practice is discouraged as it can cause compatibility issues with different versions of PHP and web servers. 

Semicolons are used as statement terminators. A statement is a single line of code that performs a specific action, such as assigning a value to a variable, calling a function, or creating a loop. A semicolon is used to mark the end of a statement and to signal to the PHP interpreter that it should move on to the next statement.

<?php phpinfo(); ?>

<?php phpinfo(); ?> is a PHP code that outputs information about the PHP installation and configuration on the web server.

When this code is executed, it generates a large table of information that includes the PHP version, server information, modules and extensions, environment variables, and more. This information can be useful for troubleshooting PHP-related issues, checking PHP configuration settings, and optimizing PHP performance.

To view the output of <?php phpinfo(); ?>, we can create a new PHP file in the web server's document root directory, add the <?php phpinfo(); ?> code to the file, and access the file using a web browser by navigating to http://localhost/filename.php, where filename.php is the name of the PHP file we created.

It is important to note that we should not leave the <?php phpinfo(); ?> code in production environments, as it can reveal sensitive information about the server and PHP installation to potential attackers. Therefore, we should only use it for debugging and troubleshooting purposes in development environments. 

<?php 

echo "<h1>Mess with the best, die like the rest.</h1>";

//echo "<h1>Second Line</h1>";

echo "Third Line";

?>

The above PHP code uses the echo statement to output text to the browser.

The first line of the code uses the echo statement to output the HTML code <h1>Mess with the best, die like the rest.</h1> to the browser. The text is enclosed in double quotes to indicate that it is a string literal.

The second line of the code is commented out using //, which means that it will not be executed by the PHP interpreter. The comment is preceded by a double slash, which indicates to the interpreter that everything on the line after the double slash should be ignored.

The third line of the code uses the echo statement to output the string literal "Third Line" to the browser. Unlike the first line, this string is not enclosed in HTML tags, so it will be displayed as plain text on the page.

This code demonstrates how to use the echo statement to output text to the browser and how to use comments to provide context and documentation for the code.

<?php 

echo "<h1>Mess with the best, die like the rest.</h1>";

/*
echo "<h1>Second Line</h1>";

echo "Third Line";
*/

?>

In programming, comments are lines of text that are added to the source code of a program to provide additional information or explanations for other developers or future reference. Comments are not executed by the program and are ignored by the interpreter or compiler.

In PHP, there are two ways to create comments:

1. Single-line comments: Single-line comments begin with two forward slashes //. Any text that follows on the same line after the // is treated as a comment and is ignored by the PHP interpreter.

Example: 

// This is a single-line comment in PHP

2. Multi-line comments: Multi-line comments are enclosed in /* and */ characters. Any text that is enclosed in these characters is treated as a comment and is ignored by the PHP interpreter.

Example: 

/* This is a multi-line comment
   in PHP that can span multiple lines */

Comments can be used to provide explanations for complex or hard-to-understand code, to document code changes, or to temporarily disable a section of code during testing or debugging. They are an important tool for making code more readable, maintainable, and understandable for other developers.