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Max Azimov
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PHP 5 Syntax
A PHP script is executed on the server, and the plain HTML result is sent back to the browser.
Basic PHP Syntax
A PHP script can be placed anywhere in the document.
A PHP script starts with <?php and ends with ?>:
  1. <?php
  2. // PHP code goes here
  3. ?>
The default file extension for PHP files is ".php".
A PHP file normally contains HTML tags, and some PHP scripting code.
Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page:
  1. <!DOCTYPE html>
  2. <html>
  3. <body>
  4. <h1>My first PHP page</h1>
  5. <?php
  6. echo "Hello World!";
  7. ?>
  8. </body>
  9. </html>
Note: PHP statements end with a semicolon (;).

Comments in PHP
A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is looking at the code.
Comments can be used to:
  • Let others understand what you are doing
  • Remind yourself of what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code
PHP supports several ways of commenting:
  1. <!DOCTYPE html>
  2. <html>
  3. <body>
  4. <?php
  5. // This is a single-line comment
  6. # This is also a single-line comment
  7. /*
  8. This is a multiple-lines comment block
  9. that spans over multiple
  10. lines
  11. */
  12. // You can also use comments to leave out parts of a code line
  13. $x = 5 /* + 15 */ + 5;
  14. echo $x;
  15. ?>
  16. </body>
  17. </html>

PHP Case Sensitivity
In PHP, all keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are NOT case-sensitive.
In the example below, all three echo statements below are legal (and equal):
  1. <!DOCTYPE html>
  2. <html>
  3. <body>
  4. <?php
  5. ECHO "Hello World!<br>";
  6. echo "Hello World!<br>";
  7. EcHo "Hello World!<br>";
  8. ?>
  9. </body>
  10. </html>
However; all variable names are case-sensitive.
In the example below, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are treated as three different variables):

  1. <!DOCTYPE html>
  2. <html>
  3. <body>
  4. <?php
  5. $color = "red";
  6. echo "My car is " . $color . "<br>";
  7. echo "My house is " . $COLOR . "<br>";
  8. echo "My boat is " . $coLOR . "<br>";
  9. ?>
  10. </body>
  11. </html>


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