Cpsc110/Notes/Starting PHP
Contents |
Introduction
This page provides a list of topics/notes based loosely on the material from Chapter 3 of Nixon, Learning PhP, MySQL, and Javascript.
Note that the book's examples are available on the website: Click here! As you are learning PHP, it would be a good practice to download and play with the examples. Just save them in a folder under your web folder, htdocs (Mac) or web (Windows), and open the examples with your browser.
Some useful references that you should consult:
PHP and HTML
PHP is embedded in HTML code by enclosing it within the <?php and ?> tags:
<HTML> <HEAD> <TITLE>Hello World</TITLE> </HEAD> <BODY> <?php echo "<P>This was printed by PHP.</P>"; ?> </BODY> </HTML>
NOTE that some PHP parsers permit "<? ... ?>" to be used as PHP tags. But this is being deprecated.
Comments
Comments are used to document and clarify your code:
<HTML> <HEAD> <TITLE>Hello World</TITLE> </HEAD> <BODY> <?php // This is a single line comment. /* * This is a multiline comment. */ echo "<P>This was printed by PHP.</P>"; ?> </BODY> </HTML>
Basic Syntax
Semicolons
PHP commands must end with a semicolon:
echo "hello world";
The $ Symbol
The '$' symbol must precede all variable names. Three different types of variables in PHP are numbers, strings, and arrays:
<?php $aNumber = 1; $aString = "Hello"; $anArray = array("one", "two", "three"); // An array of strings ?>
Variables
A variable is a memory location that stores a value of a particular type (a string such as "Hello" or a number such as 32).
A good way to think of variables is labeled matchboxes containing items.
In PHP variable names begin with $ and are defined as follows:
$variable_name = 54;
This command 'assigns' the value 54 to the variable named 'variable_name' (i.e., stores the value 54 in the matchbox labeled 'variable_name').
Variable Naming Rules
- Preceeded by '$'.
- Start with alphabetic letter or underscore (_).
- Contain only a-z, A-Z, 0-9, and underscore (_).
- No spaces.
- Case sensitive: $foo is not the same as $Foo
String Variables
<?php // test1.php // To run this example, save it in your web directory and load it // into your browser with http://localhost/web/test1.php $username = "Peggy Programmer"; echo $username; echo "<br />"; // HTML Line break $current_user = $username; echo $current_user; ?>
Numeric Variables
<?php $count = 17; $price = 17.99; ?>
Array Variables
<?php $class = array('Tiffany', 'Mark', 'Hazel', 'Grant'); $seating_plan = array(array('george', 'bill', 'john'), array('may', 'june', 'dorothy'), array('florence', 'jim', 'ted')); ?>
Variable Type
Variables in PHP are loosely typed (different from Java). A variable's type is automatically picked by PHP when you assign it a value. If you assign it a number, then its type is numeric (or integer). PHP automatically performs certain conversions--e.g., "20"/2 = 10.
Operators (PHP Manual)
Arithmetic Operators
Operator | Description | Example |
---|---|---|
+ | Addition | $j + 1 |
- | Subtraction | $j - 6 |
* | Multiplication | $j * 2 |
/ | Division | $j / 3 |
% | Modulus | $j % 2 |
++ | Increment | $++j |
-- | Decrement | $j-- |
Assignment Operators
Operator | Example | Equivalent to |
---|---|---|
= | $j = 10 | $j = 10 |
+= | $j += 5 | $j = $j + 5 |
-= | $j -= 2 | $j = $j -2 |
*= | $j *= 10 | $j = $j * 10 |
/= | $j /= 3 | $j = $j / 3 |
.= | $j .= $k | $j = $j . $k |
%= | $j %= 2 | $j = $j % 2 |
Comparison Operators
Operator | Description | Example |
---|---|---|
== | is equal to | $j == 1 |
!= | is not equal to | $j != 6 |
> | is greater than | $j > 2 |
< | is less than | $j < 3 |
>= | is greater than or equal to | $j >= 2 |
<= | is less than or equal to | $j <= $k |
Logical Operators
Operator | Description | Example |
---|---|---|
&& | And | $j == 3 && $k == 4 |
and | low-precedence and | $j == 3 and $k == 4 |
|| | Or | $j > 2 || $j < 0 |
or | low-precedence or | $j > 2 or $j < 0 |
! | Not | !($j > 5) |
xor | exlusive or | $j xor $k |
String Examples
<?php $my_string = "Margaritaville - Suntan Oil Application!"; echo "Margaritaville - Suntan Oil Application!<BR />"; echo "Time for $my_string<BR />"; $my_string = 'Margaritaville - Suntan Oil Application!'; echo $my_string; ?>
Escape Characters
<?php // \n (newline), \r (carriage return), \t (tabl), // \$ (dollar sign), \" (double quote) echo "<h2 class=\"specialH2\"Margaritaville!</h2>"; echo '<h2 class="specialH2"Margaritaville!</h2>'; ?>
Comparing Strings
String comparison operators include (PHP Manual):
operator | meaning | notes |
---|---|---|
== | equal | |
=== | identical | equal and the same type |
!= | not equal | |
!== | not identical | |
<> | not equal | |
< | less than | comes before in the alphabet |
<= | less than or equal to | |
>= | greater than or equal to | |
> | greater than |
Examples: <?php $name1 = "Bill"; $name2 = "BIll"; if ($name1 > $name2) { echo "$name1 > $name2<BR />"; } if ($name1 != $name2) { echo "$name1 != $name2<BR />"; } $number = 25; $number_string = "25"; if ($number == $number_string) { echo "$number == $number_string<BR />"; } if ($number === $number_string) { echo "$number === '$number_string'<BR />"; } else { echo "$number !== '$number_string'<BR />"; } ?>
String Concatenation
Strings can be concatenated by using the period (.) operator:
<?php $str = "This is an example of " . 3 . " in the middle of a string"; echo $str; ?>