Introduction to PHP

Introduction to PHP

• PHP stands for "PHP: Hypertext Preprocessor," a recursive acronym
• Originally named “Personal Home Page”
• PHP was developed by Rasmus Lerdorf, a software engineer and member of the Apache team
• The first part of PHP was developed in late 1994 for personal use

Usage and Integration

• By mid-1997, PHP was being used on approximately 50,000 sites worldwide
• PHP is a server-side scripting language
• PHP can be embedded in HTML or used as a stand-alone language
• Used to manage dynamic content, databases, session tracking, and even build entire E-commerce sites
• It integrates with popular databases like MySQL, PostgreSQL, Oracle, Sybase Informix, and Microsoft SQL Server
• PHP does not manage a page's looks or sounds
• Most of what PHP does is invisible to the end user
• It's an official module of the Apache HTTP Server
• PHP is fully cross-platform
• It can be natively run on several flavors of Unix, as well as on Windows and Mac OS X

Advantages of PHP

• Open Source: large community for support
• It is developed and maintained by a large group of PHP developers
• It creates a support community and an abundant extension library
• Easy to Use: especially for those familiar with C
• It uses C link Syntax
• It is easy to pick up and create website scripts
• Speed: It uses much system resource so is relatively fast
• Stable: Bugs are quickly fixed because it is maintained by many developers
• Powerful Library Support: functional modules available such as PDF and Graph
• Built-in Database Connection Modules: connects easily to databases
• Reduces web app development time
• Can be run on many platforms including Windows, Linux, and Mac
• Easy for users to find hosting service providers

Basic PHP Syntax

• A PHP file typically contains HTML tags and PHP scripting code
• PHP scripting blocks start with .
• Scripting blocks can be placed anywhere in the document
• Each code line in PHP must end with a semicolon
• Semicolons separate instructions
• echo and print are the two basic statements to output text with PHP

Escaping from HTML

• PHP parses a file, looking for opening and closing tags to start and stop code interpretation
• This allows PHP to be embedded in different documents
• Everything outside of the tags are ignored
• PHP is embedded in HTML documents

Opening and Closing Tags

• Four pairs of opening and closing tags can be used in PHP:
  • ``
  • ``
  • `` (Short Tag): Requires "short_open_tag = On"
  • <% %> (ASP Style Tag): Requires "asp_tags = on"
• ```` and `` are always available
• Short tags and ASP style tags can be turned on and off in the php.ini configuration file

PHP.ini File

• The PHP configuration file, php.ini, affects PHP's functionality
• PHP initializes the php.ini file each time
• PHP initializes it when httpd is restarted for the module version, or with each script execution for the CGI version
• Restart httpd if changes are not showing up
• Use phpinfo() to check the path to php.ini
• Keys are case sensitive
• Keyword values are not
• Whitespace and lines beginning with semicolons are ignored
• Booleans are represented by 1/0, Yes/No, On/Off, or True/False

Important settings in php.ini

• short_open_tag = Off: Required to use XML functions Short open tags look like this: ``
• disable_functions = [function1, function2...]: ability to disable selected functions for security reasons
• max_execution_time = 30: sets the time limit for script execution
• set_time_limit() won’t work in safe mode
• Abort based on maximum memory consumed in Windows
• Apache timeout setting will also apply to non-PHP files on the site error_reporting = E_ALL & ~E_NOTICE
• The default value is E_ALL & ~E_NOTICE, all errors except notices
• Development servers should be set to at least the default, only production servers should even consider a lesser value
• auto-prepend-file = [path/to/file]: PHP must automatically include() it at the beginning of every PHP file, include path restrictions apply
• auto-append-file = [path/to/file]: PHP must automatically include() it at the end of every PHP file, include path restrictions apply
• file_uploads = [on/off]: Turn on this flag to upload files using PHP script
• mysql.default_host = hostname: default server host connecting host if host not specified
• mysql.default_user = username: default username for connecting to database
• mysql.default_password = password: default password for connecting to database

.htaccess in PHP

• .htaccess is a configuration file for web servers running on the Apache web server software
• When placed in a directory, it's loaded by the Apache web server
• .htaccess files modify the setup of Apache to empower additional features, various configurations
• .htaccess empower Apache server functionality

PHP Variables

• PHP variables start with a dollar sign ($)
• Variable names are case-sensitive
• Variable names must start with a letter or underscore, followed by letters, numbers, or underscores

Variable Scope

• Variable scope is the context in which it is defined
• PHP variables mostly have a single scope
• User-defined functions introduce a local function scope
• Variables used inside functions are limited to the local function scope by default unless globalized

The "global" Keyword

• PHP global variables used in functions must be declared global inside the function using the "global" keyword or the $GLOBALS array
• Declaring variables as global within the function makes all references to them refer to the global version

Using Static Variables

• Static variables exist only in the local function scope
• Static variables do not lose their value when program execution leaves the scope
• It sets $a to 0 and prints "0", which is useless as the $a++ serves no purpose and the $a variable disappears as soon as the function exits
• Declaring $a as static makes Test() retain current count

Variables from outside PHP (HTML Forms GET and POST)

• Information from a submitted form becomes automatically available to the PHP script
• GET and POST methods for form objects

GET Method

• The GET method passes arguments as part of the URL (Uniform Resource Locator) Query String
• When you use form handling, GET then appends the indicated variable name and value to the designated URL in the ACTION attribute
• it uses a question mark separator
• Each item that you submit goes through the GET method in the $_GET array

Advantage of GET Method

• Advantage: It constructs a differentiated URL query string so the user can bookmark the page

Disadvantages of GET Method

• GET is not suitable for login forms because username & password are fully visible on screen
• Every GET submission is recorded in the web server log, data set included
• There is a limit to the URL's length, so there is a limit to the data passed using GET method

POST Method

• Generally POST method is the better option for form submissions
• The form dataset is included in the body of form when forwarded to the processing agent which is the web server
• There is no visible change to the URL that results to the data that has been submitted
• Each item you submit via the POST method goes to the handler via the $_POST array

Advantages of POST Method

• POST method is a way more secure option because the user's entered information is never visible in the URL
• There is a larger limit on the amount of data that you can pass which is a couple of kilobytes

Disadvantage of POST Method

• The results at a given cannot be bookmarked
• If the result expires from the browser's memory then the user can't revisit the page
• There may be an error when employing Back button to revisit page
• This method may be incompatible with certain firewall setups

PHP Operators

• Operators are used in expressions where operands are being evaluated
• Operators perform a calculation on each operand
• Ex. 4 + 5 is equal to 9.
• The "4" and "5" here are the operands, and add is what the "+" is

Arithmetic Operators

• Arithmetic operators add, subtract, multiply, divide, modulus
• + Adds two operands
• - Subtracts second operand from the first
• * Multiply both operands
• / Divide numerator by de-numerator
• % Modulus Operator and remainder after an integer division
• ++ Increment operator increasing integer by one
• -- Decrement operator decreasing integer by one

Comparison Operators

• Comparison operators are comparing values, true or not true
• Equal, Not Equal, Greater Than, Less Than
• If conditions match, expression is true

Logical Operators

• Logical operators determine logic and order
• AND, OR, NOT
• Based on the other condition, the outcome switches, like NOT's false/true switching

Assignment Operators

• Assign values from left to right
• If A is being added to B then assigned to C, then C becomes B

Conditional Operators

• First evaluates expression for "true/false", then statements depending on result of expression are executed

Operator Categories

• All the operators can be categorised into Unary prefix operator, Binary operators, Ternary Operators and Assignment Operators.
• Unary prefix operators, which precede a single operand
• Binary operators, which take two operands and perform a variety of arithmetic and logical operations
• Conditional operator (a ternary operator), which takes three operands and evaluates either the second or third expression, depending on the evaluation of the first expression
• Assignment operators, which assign a value to a variable

Precedence of PHP Operators

• Operator precedence determines order of operations in an expression
• Multiplication has higher precedence than addition
• Ex: 7 + 3 * 2 is 13, not 20, because Operator "*" is performed first

Control Structures/Decision Making

• If, elseif...else, and switch statements are used to make decisions based on different conditions
• Statement that is to be executed with the different conditions

If...Else Statement

• In case some code is to be executed when conditions are met or not met

if (condition) {
  code to be executed if condition is true;
} else {
  code to be executed if condition is false;
}

• Output "Have a nice weekend!" if current date is Friday

ElseIf Statement

• In case some code is to be executed if one of several conditions are true

if (condition) {
  code to be executed if condition is true;
} elseif (condition) {
  code to be executed if condition is true;
} else {
  code to be executed if condition is false;
}

• Output "Have a nice weekend!" if the current day is Friday, otherwise, it will output "Have a nice day!".

Switch Statement

• Switch Statement is for when you want to choose one of many code blocks
• Avoids Long if...elseif...else block statements

switch (expression){
    case label1:
     code to be executed if expression = label1;
     break;
     case label2:
     code to be executed if expression = label2;
     break;
     default:
     code to be executed
    if expression is different
    from both label1 and label2;
}

Control Statements

• Loops in PHP are used to execute the same block of code a specified number of times
• Four Loop Types:
  • for loops
  • while loops
  • do...while loops
  • foreach loops

For Loop

• Loops a certain number of times

for (initialization; condition; increment){
    code to be executed;
}

• the initializer sets the initial loop cycle count, normally called $i

While Loop

• While the condition is true, the code in block will be executed repeated

while (condition) {
    code to be executed;
}

• The test code is tested first

Do..While Loops

• The statement will execute at least once first before any re-execution later

do {
  code to be executed;
}
while (condition);

• The testing part is at the end

ForEach Loops

• ForEach is used to loop through arrays

foreach (array as value) {
    code to be executed;
}

• ForEach goes through a value sequence

Using the Break Statement

• Terminate the execution of a loop early using break keywords
• Provides complete control over loop behavior
• For conditional loops, it will always be an option to come out

Using the Continue Statement

• Halt current iteration of loop, but not terminate it unlike break
• Just like the break statement, continue is situated inside the statement block
• But it's preceed by conditional

Arrays

• Collection of multiple things into one
• It is easy to define a bunch of variables as elements of a single array

      Numeric array – An array with a numeric index. Values are stored and accessed in linear fashion.
      Associative array – An array with strings as index. This stores element values in association
         with key values rather than in a strict linear index order.
      Multidimensional array – An array containing one or more arrays and values are accessed
         using multiple indices

User Defined Functions

• User-defined functions are not requirement in PHP
• If there are many code files, it may be indication that functions should be used

What is a Function

• Way of wrapping section of code & name
• Like methods from other languages

function function-name ($argument-1 ,$argument-2..)
 {
        statement - 1;
        statement - 2; ...
 }

• Function definition has four parts:
  • The special word function
  • The name that you want to give your function
  • The function’s parameter list-dollar-sign variable separate by commas
  • The function body – a brace-enclosed set of statements
• Function naming rule: rules on parameters
• Function parameter information can be passed via arguments
• PHP supports passing arguments:
• by value (default)
• by reference
• default argument values
• variable-length argument lists

Making Passing be by Referencing

• By default, arguments are passed by value
• Using ampersand (&) gives code access

Default Arguments

• Ability to have default values
• Must define right
• Must define any arguments with default value to the right of any arguments without default value

PHP Variable Length Argument Function

• PHP supports variable length argument function. It means you can pass 0, 1 or n number of arguments in function
• Use ellipses (...): three dots
• PHP 5.6 implements three dot concept
• Number of arguments must be specific: numargs = func_num_args();

Built-In Functions

• Variable Functions

  • gettype() returns data type of a variable
  • settype(variable,datatype) changes variable
  • isset() checks if value is or is not set in variable
  • unset() Destroys variable
  • strval() Converts var to string
  • floatval() Converts var to float
  • intval() Converts var to int
  • print_r() print structure of array

• String function

  • chr() converts ASCII value to character
  • ord() converts character to ASCII value
  • strtolower() lowercase a string
  • strtoupper() uppercase a string
  • strlen() counts character
  • ltrim() remove spaces or char at left side of string
  • rtrim() remove spaces or char at right side of string
  • trim() remove spaces at both side

• Math functions

  • abs() returns abs value of number
  • ceil() returns upper value of float
  • floor() returns lower vat of float
  • round() returns rounded value
  • fmod()
  • min() returns lowest valued parameters
  • max() returns highest valued parameters
  • pow() x to power of y

  • sqrt() Returns square root
    

  • rand() returns andom number
  • sin() sin
  • cos() cos
  • tan() tan
  • asin() arcsin
  • acos() arccos
  • atan() arctan
  • is_infinite checks if value is infinity
  • is_finite checks if value is finite or not
  • deg2rad() convert number of degrees to corresponding number of radians
  • decbin() converts decimal to bin
  • bindec()
  • hexdec()
  • dechex()
  • base_convert()

• Array

  • count() elements available
  • list() creates numbered variables
  • in_array value in arr or not
  • current() the pointed node
  • next() moves the pointer to next
  • prev() moves to previous
  • end() moves to end of the array
  • each() current + moves
  • stristr()
  • sort() sorted

• File Handling

  • File Open Modes fopen() - Open and Read File - Open and Write File - Check - Close - FileExists - is_readable - is_writable

• String function - File

       -   Get contents
       -   put contents
  

• String Manipulation -String compare - string replace 12 Miscellaneous function : - Header File - Include - die()/ exit - constants

• Date and time functions

Single vs Double quotes

• single quotes does not interpret escape sequences but double quotes
• variables in code do not expand in Single Quotes, only complex variables in double
• simple way to enclose string in single quotes

PHP Call by Value/Reference

• Call function reference and value

PHP call by value,
actual value is unmodified inside.
PHP call by reference,
actual value modified inside.