<?php
  $myname = "George";
  $myage = 27;
  echo "a: " . 73      . " <br />" // Numeric literal
  echo "b: " . "Hello" . " <br />" // String literal
  echo "c: " . FALSE   . " <br />" // Boolean literal
  echo "d: " . $myname . " <br />" // Variable string literal
  echo "e: " . $myage  . " <br />" // Variable numeric literal
?>

These return:
a: 73
b: Hello
c: // false so nothing
d: George
e: 27

In conjunction with operators, it’s possible to create more complex expressions that evaluate to useful results…

When you combine assignment of control-flow constructs with expressions, the result is a statement.

<?php
  $daysToNewYear = 366 - $dayNumber ; // Expression
 &nbsp:   if ($daysToNewYear < 30 )
      {
        echo "Not long to go now until new year!"; //Statement
      }
?>

y = 3(abs(2x) + 4)

In PHP

  $y = 3 * (abs(2 * $x) + 4);

The value returned (y or $y in this case) can be a number, string or a Boolean value.

Boolean is TRUE or FALSE, 5 == 6 is FALSE

Uppercase Booleans can be redefined. Lowercase cannot.

Some booleans:

<?php
  echo "a : [" . ( 20 < 9 ) . "] <br />",
  echo "b : [" . ( 5 == 6 ) . "] <br />",
  echo "c : [" . ( 1 == 0 ) . "] <br />",
  echo "d : [" . ( 1 == 1 ) . "] <br />",
?>

The output of this code would be:

a: [1]
b: []
c: []
d: [1]

Notice that both expressions a and d evaluate to true, which has a value of 1. But b & c evaluated to false don’t show anything because PHP FALSE is defined as NULL or nothing.

Global variables can be called by any function. All your code can access them.

Static Variables can be sued to keep track of how many times a function has been called. It’s contents are not wiped when the function has ended unlike a local variable.

Superglobal variables are predefined variables and contain lots of useful information about the current running program and it’s environment.

Superglobals are often used by hackers trying to find exploits to break into your website. You should always sanitise superglobals before using them… the htmlentities function is a good way to do this.

  $came_from = htmlentities( $_SERVER['HTTP_REFERRER'] );

<?php
  function longdate($timestamp)
  {
    return date("l F jS Y", $timestamp);
  }
?>

To output today’s date with this function, place the following in your code:

  echo longdate( time() );

This call uses the built in PHP time function to fetch the current unix timestamp and passes it the the new longdate function, which returns the appropriate string the the echo command for display.

  $b ? print "TRUE" : print "FALSE";

One example for a constant might be to hold the location of your server root (containing the files of your website) like this:

  define("ROOT_LOCATION", "/user/local/www/");

To read it’s contents you refer to it like a variable (but it isn’t proceeded by the $):

  $directory = ROOT_LOCATION;

Now when you need to run your code on a different server, you only need to change one line of code.

Use uppercase for constants. It’s good practice.

<?php
  $author = "George Phillips";

  This is line one
  This is line two
  Written by $author." ;
?>

Or

<?php
  $author = "George Phillips";

  This is line one
  This is line two
  Written by $author.";
?>

PHP also offers a multiline sequence using the <<< operator commonly referred to as here-document or heredoc for short.

<?php
  $author = "George Phillips";

  _END;
?>

This outputs everything between the _END tag if it were a double quoted string. So you can write entire sections of HTML in PHP code and just replace specific dynamic posts with PHP variables.

The closing _END; tag MUST appear right at the start of a new line and the only thing on the line. Not ever a comment is allowed.