PROWAREtech
PHP: Tutorial - Page 1
Entering and Exiting PHP Mode
PHP code is embedded in the HTML so all pages are capable of processing and containing HTML. PHP considers all text it finds in the file to be HTML until it finds one of four things:
<?php<?<%<script language="php">
To exit PHP mode, use ?>, %> or </script>. This tutorial will use <?php.
Here is an example PHP file:
<html>
<head>
<title>
<?php
echo 'HELLO PHP!';
?>
</title>
</head>
<body>
<?php
// THIS IS A COMMENT
for($i = 0; $i < 10; $i++) {
echo $i.'<br />';
}
?>
</body>
</html>
echo is a language construct that writes to standard output. The print function can be used identically.
Variables
All PHP variables start with a dollar sign ($). They are interchangeable which means PHP is a weakly typed language because
it does not have different types of variables. One variable handles numbers, strings, booleans, arrays, etc. In the above example,
$i is a variable and the keyword echo outputs data to the screen.
integer, float, string and boolean are simple types. array,
object and resource are complex types.
Strings
Strings are simply an array of bytes (ASCII, not UTF-8). Example strings are 'this is a test', "this is a test", and even numbers when inside of quotes "0123456789".
Single Quote Strings
Single quote strings like 'this is a single quote string' have only two special characters that need to be escaped: the single quote and the
backslash. As a result, single-quoted strings are more efficient. For example, 'I\'ll go to the C:\\ drive or lose $20.' would
print this:
I'll go to the C:\ drive or lose $20.
Double Quote Strings
This table shows the double-quoted string escape sequences:
| escape sequence |
character |
|---|---|
| \n | newline |
| \r | carriage return |
| \t | tab |
| \\ | backslash |
| \$ | dollar sign |
| \" | double quote |
| \0 to \777 | octal value |
| \x0 to \xFF | hex value |
For example, the string "The so called \"car\"\ncost \$25,999!" would print this:
The so called "car" cost $25,999!
Variable Substitution
Double quote strings feature variable substitution. Single quote strings do not have this making them faster. Run this script to compare them.
<?php
$num = 14;
echo "I have $num plants.";
echo 'I have $num plants.';
?>
Objects
Objects are used to define and manipulate a set of variables that belong to a unique entity. Each object has it own set of variables and functions that operate on those variables.
Resources
PHP has many extensions available to it that allow it to manipulate graphics, connect to databases, or make calls to Java programs. Because these are external systems then they need to have types of data unique to them that PHP cannot represent using any of the other data types. These data types are meaningless to PHP but can be used by the external libraries that created them.
Arrays
An array is made up of many elements. Each element has a key that defines its place in the array. An array can have only one element with a given key. Each element also has a value, which is the data associated with the key. Finally, each array has a cursor, which points to the current key.
Keys can be almost anything: integers, objects, strings, or other arrays. Floating-point numbers may not be used as keys.
Use the pseudo-function array to create a new array and the [] operator to add items to an array.
<?php
$a = array();
$a[2] = "HELLO"; // key equals 2
$a[] = "PHP!"; // no key
$a["jackpot"] = "win"; // key equals "jackpot"
$a["test"] = array(0 => "YES!"); // key equals "test", value is an array; 0 is a key, "YES!" is the value
$a["test"][1] = "NO!"; // multi-dimensional array
echo $a[2];
echo $a["jackpot"];
echo $a["test"][0];
echo $a["test"][1];
?>
Determining the Data Type
Use the gettype function to return the type of a variable. Valid return values are 'integer', 'string', 'double', and 'object'.
gettype takes one parameter: a variable to evaluate.
