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Chapter 3 Introduction to PHP. By default, PHP documents end with the extension . php files ending with . htm or .html to also get parsed by the PHP processor

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incorporating php within html

By default, PHP documents end with the extension .php

  • files ending with .htmor .html to also get parsed by the PHP processor
  • To trigger the PHP commands, you need to learn a new tag. The first part is: <?phpthe closing part is encountered, which looks like this: ?>
Incorporating PHP Within HTML
calling the php parser

A small PHP “Hello World” program might look like


echo "Hello world";


  • all the examples from this book have been archived onto a specially created companion website at
Calling the PHP Parser
using comments

There are two ways in which you can add comments

  • // This is a comment
  • after a line of code $x += 10; // Increment $x by 10
  • When you need multiple-line comments


/* This is a section

of multiline comments

which will not be

interpreted */


Using Comments
basic syntax


$x += 10;

You must place a $ in front of all variables


$mycounter = 1;

$mystring = "Hello";

$myarray = array("One", "Two", "Three");


Basic Syntax
understanding variables

String variables $username = "Fred Smith";

<?php // test1.php

$username = "Fred Smith";

echo $username;

echo "<br />";

$current_user = $username;

echo $current_user;


Understanding Variables
numeric variables

$count = 17; to store the number 17 in the variable $count

  • $count = 17.5; a floating-point number (containing a decimal point);
  • Arrays $team = array('Bill', 'Joe', 'Mike', 'Chris', 'Jim');
  • Two-dimensional arrays


$oxo = array(array('x', '', 'o'),

array('o', 'o', 'x'),

array('x', 'o', '' ));


Numeric variables
variable naming rules

four rules:

  • • Variable names must start with a letter of the alphabet or the _ (underscore) character.
  • • Variable names can contain only the characters: a-z, A-Z, 0-9, and _ (underscore).
  • • Variable names may not contain spaces. If a variable must comprise more than one word it should be separated with the _ (underscore) character. (e.g., $user_name).
  • • Variable names are case-sensitive. The variable $High_Score is not the same as the variable $high_score.
Variable naming rules

Operators are the mathematical, string, comparison, and logical commands such as plus, minus, times, and divide. PHP looks a lot like plain arithmetic; for instance, the following statement outputs 8:

echo 6 + 2;

variable assignment

The syntax to assign a value to a variable is always variable = value. Or, to reassign the value to another variable, it is other variable = variable.

  • Variable incrementing and decrementing
  • String concatenation uses the period (.) to append one string of characters to another. The simplest way to do this is as follows:

echo "You have " . $msgs . " messages.";

Variable Assignment
multiple line commands

Example 3-6. A multiline string echo statement


$author = "Alfred E Newman";

echo "This is a Headline

This is the first line.

This is the second.

Written by $author.";


Multiple-Line Commands
variable typing

Variables do not have to be declared before they are used, and that PHP always converts variables to the type required by their context when they are accessed.

Variable Typing

Constants are similar to variables, holding information to be accessed later, except that they are what they sound like—constant

e cho and print commands

echo cannot be used as part of a more complex expression, whereas print can

$b ? print "TRUE" : print "FALSE";

  • The question mark is simply a way of interrogating whether variable $b is true or false. Whichever command is on the left of the following colon is executed if $b is true, whereas the command to the right is executed if $b is false
Echo and print Commands

A simple function declaration


function longdate($timestamp)


return date("l F jS Y", $timestamp);



a function using a static variable


function test()


static $count = 0;

echo $count;




A function using a static variable