PHP Intro

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PHP Introduction

1. Running PHP from the Command Line

Follow these directions to run PHP from the command line on a PC with php-cgi installed.
Running PHP from the command line per se is not possible on ectweb, but you can output results to the HTML document instead by using a code block like this:
<?php
    $x = 1;
    $y = 2;
    $sum = $x + $y;
    echo $sum;
?>
The code delimited by <?php and ?> is called a code island.
PHP code islands can be dropped anywhere in an HTML document.

2. The echo Statement

The echo statement prints its arguments
If more than one argument is passed to echo, the arguments are separated by commas:
echo 1,"abc",2
The output is
1abc2
The print statement is similar to echo but more restrictive. It only allows one argument:
print "abc"

Comments

PHP supports three kinds of comments:

3. Datatypes

PHP supports eight datatypes:

Datatype Description or Examples

boolean
TRUE or FALSE Internally, TRUE is represented as 1,
FALSE is represented as the empty string.

integer 3542, 0, -143, ...

float

3.14159, 2.7128, -45.0, 3.283e17, ...

string "hello", 'abc', " " (space), "" (empty string), ...

array Holds a list of items.

object Holds an object instance created from a class.

resource

Holds an resource such as a file, image or database.

null
Represents an uninitialized variable.
Its only possible value is NULL.

Strings can be delimited by either single or double quotes.
Like strings in .Net or Java, PHP strings are immutable.

Datatype	Description or Examples
boolean	TRUE or FALSE Internally, TRUE is represented as 1, FALSE is represented as the empty string.
integer	3542, 0, -143, ...
float
3.14159, 2.7128, -45.0, 3.283e17, ...
string	"hello", 'abc', " " (space), "" (empty string), ...
array	Holds a list of items.
object	Holds an object instance created from a class.
resource
Holds an resource such as a file, image or database.
null	Represents an uninitialized variable. Its only possible value is NULL.

A string can also be defined using the heredoc syntax:

$s = <<<END
<html>
<body>
<p>Hello</p>
</body>
</html>
END;

Instead of single or double quotes, the starting is <<<END and the ending token is END where the characters END are chosen by the programmer.
The heredoc ending token must not be indented and must be followed by a semicolon.

These special characters are available when used inside double quote delimited strings:

\n  New Line
\r  Carriage Return
\t  Horizontal Tab
\\  Backslash
\$  Dollar Sign
\"  Double Quote

4. Variables

A variable contains a value of one of the eight datatypes listed in the previous section.
Variables are not declared in PHP.
PHP variable names always begin with $.
The second character of a variable name can be a letter (upper or lowercase) or an underscore.
The remaining characters of a variable name can be a letter, digit or an underscore.
Examples of variable names:
$x $x2 $_x5 $_3_ $pizza_temperature $_3rd_planet_from_the_sun
Variable names are case sensitive. However, variable names that only differ in case are not recommended.
Use the assignment operator to set or change the value of a variable:
$x = 5;
Variables are interpolated into a double quoted string:
<?php
$numb_items = 45;
$output = "The number of items is $numb_items."
echo $output;
?>
produces the output
The number of items is 45.
Caution: variables are not interpolated into single quoted strings.
If there is no space between a variable name and the next character in the double quoted string, use braces to delimit the variable name. This example produces an undefined variable error
<?php
$text = "news";
$output = "Where's the $textpaper?";
?>
Using braces produces the correct result:
<?php
$text = "paper";
$output = "Where's the {$text}paper?";
echo $output;
?>
The output is
Where's the newspaper?
PHP also allows variable variables, that is variables that contain variable names:
<?php
$raccoons = 7;
$animalname = "raccoons";
echo "The number of $animalname is ", $$animalname, ".";
?>
The output is
The number is raccoons is 7.
To allow correct interpolation of variable variables in double quoted strings, use braces:
<?php
$raccoons = 7;
$animalname = "raccoons";
echo "The number of $animalname is ${$animalname}.";
?>
The output is
The number of raccoons is 7.

5. Operators

Some PHP operators:
A table of these PHP operators with descriptions.
An operator precedence table.

6. Arrays

An array in PHP is a list of items that can be accessed by a string or numeric key.
A PHP array is more like a VB array list or hashtable than it is like a VB array.
Items can be inserted into an array in three ways:
1. By numeric key:
  $a[3] = "xyz";
2. By string key:
  $a["dog"] = 342530;
3. Using the array function:
  $a = array("xyz", 342530, 3.4565);
  The default indices are 0, 1 and 2.
4. Using the array function:
  $a = array(3 => "xyz", "dog" => 342530, 3.4565);
  The indices are 3, "dog" and 0.
To append an item to the end of an array:
$a[ ] = "xyz";
To access an array item, use its key:
echo $a["dog"];
To modify an array item, use its key:
$a["dog"] = 657645;
To remove an item from an array, use the unset function:
unset($a["dog"]);
Here are some PHP array functions.
The following operators can be used on arrays:
+ (concatenate) == (same elements) === (identical to) != <> !==
Use this online reference as a manual for all documented PHP functions:
http://www.php.net/quickref.php

7. String Handling Functions

Here is a table of some string handling functions.
Use this online reference as a manual for all documented PHP functions:
http://www.php.net/quickref.php

7. Casting

Casting means convert from one datatype to another.
Here are some PHP casting operators:
(int) (float) (string) (boolean) (array)
Many of the casting operations are self explanatory. Here are some that require comment:

7. Control Structures

PHP contains these control structures:
if..else, while, for, for each, switch.
The syntax of if..else, while and switch is identical to Java/C++.
PHP has an alternate syntax for if..else and while statements similar to VB.Net.
See this document for the Syntax of PHP Control Structures.

8. Builtin Functions

Here are some more builtin functions: