PHP Data Types

Two Data Type Categories

1. Scalar - contains only one value at a time


2. Composite or Compound - array and objects

Four scalar types supported

1. boolean - a value that can only either be true or false


2. int - a signed numeric integer value


3. float - a signed floating-point value


4. string - a collection of binary data

Numeric Values

PHP recognizes two types of numbers

1. integers
   - the int data type is used to represent signed integers


2. floating-point values
   - also called float and sometimes double, are numbers that have a fractional component

Numeric Notations

1. Decimal - standard decimal notation.
   ex. 10; -11; 1452
   Note: no thousand separator is needed or allowed


2. Octal - identified by its leading zero (like the access permission of Unix)
   ex. 0666, 0100


3. Hexadecimal
   ex. 0x123, 0XFF; -0x100

Note
The leading 0x prefix are both case-insensitive
Note
Octal numbers can easily confused with decimal numbers and can lead to some consequences

Two supported notations for Floating-point numbers

1. Decimal - traditional decimal notation
   ex. 0.12; 1234.43; -.123


2. Exponential - composed of a mantissa value followed by a case-insensitive letter E then an exponent value.
   ex. 2E7, 1.2e2

Note

1. The precision and range of both types varies depending on the platform on which your scripts run
   ex. 64-bit platforms may be capable of representing a wider range of integer numbers than 32-bit platforms


2. PHP doesn't tract overflows


3. Float data type is not always capable of representing numbers in the way you expect it to.
   ex. echo (int)((0.1 + 0.7) * 10);
   this results to 7 instead of 8 since the result of this simple arithmetic expression is stored internally as 7.999999 instead of 8.0.

Strings

An ordered collection of binary data.

• could be text, content of an image file, spreadsheed or even a music recording.

Booleans

• can only contain either TRUE or FALSE.


• used as basis for logical operations.

Note
When converting data to and from the Boolean type, several rules apply:

1. When a numeric variable is converted to boolean data type, the value becomes false if the variable contains zero and true otherwise.


2. When a string variable is converted to boolean data type, the value becomes false only when the variable is empty or if it contains a single character 0. Other values, it is converted to true.


3. When a boolean variable is converted to a numeric or string, it becomes 1 if it is true, and 0 otherwise.

Anatomy of a PHP Script

• every PHP script is made up of statements.


• each statement must be terminated with a semicolon.
  Example:
  
some_instruction();
$variable = 'value';
  

Note:

The last instruction before a closing tag does not require a semicolon, but it is advisable to always terminate an instruction with a semicolon.

Comments

Types of PHP comments:

1.  // Single line comment




2.  # Single line comment




3.  /* Multi-line
       comment
     */




4.  /**
     * API Documentation Example
     *
     * @param string $bar
     */
     function foo($bar) { }

Note:

Because the closing tag ?> will also end a comment, code like:

// Do not show this ?> or this 

will output:

or this

• because the single line comment was terminated by ?>


• Normally, a single line comment should be terminated with a newline (\r, \n or \r\n)

Whitespace

PHP is whitespace-insentive, except with this few limitations:

1. You cannot have any whitesapce between <? and php


2. You cannot break apart keywords
   ex. whi le, fo r, and funct ion


3. You cannot break apart variable names and function names
   ex. $var name and function foo bar()

Code Block

A series of statements enclosed between two braces:

{
    // some comments 
    f(); // a function call
}

• used in creating groups of script lines that must all be executed under specific circumstances, such as a function call or a conditional statement.


• code blocks can be nested.

Language Constructs

Elements that are built-into the language that follow specific rules.
Ex.

   echo 10; // will output 10
   print (10); // will also output 10
   exit(); // terminate the script and either output a string or return a numeric status 
   die();   // an alias of exit()

Note:

echo is not a function and therefore does not have a return value

PHP Syntax

• simple and easy to understand.


• derived from many languages but most of it were from C and some from Perl.


• its object-oriented syntax were patterned from Java and C++.

Source Files and PHP Tags

PHP code can be inserted directly into a text file using a special set of tags; the interpreter will then output any text outside the tags as-is, and execute the code that is between the tags.

4 Types of Tags

1. Standard Tags
   

   
   <?php
   ... code
   ?>
   

   
   


2. Short Tags
   

   
   <?
   ... code
   ?>
   <?= $variable ?>
   

   
   


3. Script Tags
   

   
   <script language="php">
   ... code
   </script>
   

   
   


4. ASP Tags
   

   
   <%
   ... code
   %>
   

   
   

Note:

3 and 4 are all considered deprecated.

Note:

To prevent spurious output from an include file, omit the closing tag at the end