Tuesday, May 3, 2016

PHP 5 : PHP 5 Operators PHP OperatorsOperators are used to...

PHP 5 : PHP 5 Operators PHP OperatorsOperators are used to...: PHP 5 Operators PHP Operators Operators are used to perform operations on variables and values. PHP divides the operators in the ...

PHP 5 Functions

The real power of PHP comes from its functions; it has more than 1000 built-in functions.

PHP User Defined Functions

Besides the built-in PHP functions, we can create our own functions.
A function is a block of statements that can be used repeatedly in a program.
A function will not execute immediately when a page loads.
A function will be executed by a call to the function.

Create a User Defined Function in PHP

A user defined function declaration starts with the word "function":

Syntax

function functionName() {
code to be executed;
}

Note: A function name can start with a letter or underscore (not a number).
Tip: Give the function a name that reflects what the function does!

	Function names are NOT case-sensitive.

In the example below, we create a function named "writeMsg()". The opening curly brace ( { ) indicates the beginning of the function code and the closing curly brace ( } ) indicates the end of the function. The function outputs "Hello world!". To call the function, just write its name:

Example

<?php
function writeMsg() {
echo "Hello world!";
}

writeMsg(); // call the function
?>

PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.
Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.
The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

Example

<?php
function familyName($fname) {
echo "$fname Refsnes. ";
}

familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>

PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

Example

<?php
function setHeight($minheight = 50) {
echo "The height is : $minheight ";
}

setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>

PHP Functions - Returning values

To let a function return a value, use the return statement:

Example

<?php
function sum($x, $y) {
$z = $x + $y;
return $z;
}

echo "5 + 10 = " . sum(5, 10) . " ";
echo "7 + 13 = " . sum(7, 13) . " ";
echo "2 + 4 = " . sum(2, 4);
?>

PHP 5 Arrays

An array stores multiple values in one single variable:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
?>

What is an Array?

An array is a special variable, which can hold more than one value at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

$cars1 = "Volvo";
$cars2 = "BMW";
$cars3 = "Toyota";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The solution is to create an array!
An array can hold many values under a single name, and you can access the values by referring to an index number.

Create an Array in PHP

In PHP, the array() function is used to create an array:

array();

In PHP, there are three types of arrays:

Indexed arrays - Arrays with a numeric index
Associative arrays - Arrays with named keys
Multidimensional arrays - Arrays containing one or more arrays

PHP Indexed Arrays

There are two ways to create indexed arrays:
The index can be assigned automatically (index always starts at 0), like this:

$cars = array("Volvo", "BMW", "Toyota");

or the index can be assigned manually:

$cars[0] = "Volvo";
$cars[1] = "BMW";
$cars[2] = "Toyota";

The following example creates an indexed array named $cars, assigns three elements to it, and then prints a text containing the array values:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
?>

Get The Length of an Array - The count() Function

The count() function is used to return the length (the number of elements) of an array:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
echo count($cars);
?>

Loop Through an Indexed Array

To loop through and print all the values of an indexed array, you could use a for loop, like this:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
$arrlength = count($cars);

for($x = 0; $x < $arrlength; $x++) {
echo $cars[$x];
echo " ";
}
?>

PHP Associative Arrays

Associative arrays are arrays that use named keys that you assign to them.
There are two ways to create an associative array:

$age = array("Peter"=>"35", "Ben"=>"37", "Joe"=>"43");

or:

$age['Peter'] = "35";
$age['Ben'] = "37";
$age['Joe'] = "43";

Loop Through an Associative Array

To loop through and print all the values of an associative array, you could use a foreach loop, like this:

Example

<?php
$age = array("Peter"=>"35", "Ben"=>"37", "Joe"=>"43");

foreach($age as $x => $x_value) {
echo "Key=" . $x . ", Value=" . $x_value;
echo " ";
}
?>

PHP 5 Sorting Arrays

The elements in an array can be sorted in alphabetical or numerical order, descending or ascending.

PHP - Sort Functions For Arrays

In this chapter, we will go through the following PHP array sort functions:

sort() - sort arrays in ascending order
rsort() - sort arrays in descending order
asort() - sort associative arrays in ascending order, according to the value
ksort() - sort associative arrays in ascending order, according to the key
arsort() - sort associative arrays in descending order, according to the value
krsort() - sort associative arrays in descending order, according to the key

Sort Array in Ascending Order - sort()

The following example sorts the elements of the $cars array in ascending alphabetical order:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
sort($cars);
?>

Example

<?php
$numbers = array(4, 6, 2, 22, 11);
sort($numbers);
?>

PHP 5 Global Variables - Superglobals

Superglobals were introduced in PHP 4.1.0, and are built-in variables that are always available in all scopes.

PHP Global Variables - Superglobals

Several predefined variables in PHP are "superglobals", which means that they are always accessible, regardless of scope - and you can access them from any function, class or file without having to do anything special.
The PHP superglobal variables are:

$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION

This chapter will explain some of the superglobals, and the rest will be explained in later chapters.

PHP $GLOBALS

$GLOBALS is a PHP super global variable which is used to access global variables from anywhere in the PHP script (also from within functions or methods).
PHP stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable.
The example below shows how to use the super global variable $GLOBALS:

Example

<?php
$x = 75;
$y = 25;

function addition() {
$GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
}

addition();
echo $z;
?>

PHP $_SERVER

$_SERVER is a PHP super global variable which holds information about headers, paths, and script locations.
The example below shows how to use some of the elements in $_SERVER:

Example

<?php
echo $_SERVER['PHP_SELF'];
echo " ";
echo $_SERVER['SERVER_NAME'];
echo " ";
echo $_SERVER['HTTP_HOST'];
echo " ";
echo $_SERVER['HTTP_REFERER'];
echo " ";
echo $_SERVER['HTTP_USER_AGENT'];
echo " ";
echo $_SERVER['SCRIPT_NAME'];
?>

The following table lists the most important elements that can go inside $_SERVER:

Element/Code	Description
$_SERVER['PHP_SELF']	Returns the filename of the currently executing script
$_SERVER['GATEWAY_INTERFACE']	Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER['SERVER_ADDR']	Returns the IP address of the host server
$_SERVER['SERVER_NAME']	Returns the name of the host server (such as www.w3schools.com)
$_SERVER['SERVER_SOFTWARE']	Returns the server identification string (such as Apache/2.2.24)
$_SERVER['SERVER_PROTOCOL']	Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER['REQUEST_METHOD']	Returns the request method used to access the page (such as POST)
$_SERVER['REQUEST_TIME']	Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER['QUERY_STRING']	Returns the query string if the page is accessed via a query string
$_SERVER['HTTP_ACCEPT']	Returns the Accept header from the current request
$_SERVER['HTTP_ACCEPT_CHARSET']	Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER['HTTP_HOST']	Returns the Host header from the current request
$_SERVER['HTTP_REFERER']	Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER['HTTPS']	Is the script queried through a secure HTTP protocol
$_SERVER['REMOTE_ADDR']	Returns the IP address from where the user is viewing the current page
$_SERVER['REMOTE_HOST']	Returns the Host name from where the user is viewing the current page
$_SERVER['REMOTE_PORT']	Returns the port being used on the user's machine to communicate with the web server
$_SERVER['SCRIPT_FILENAME']	Returns the absolute pathname of the currently executing script
$_SERVER['SERVER_ADMIN']	Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as someone@w3schools.com)
$_SERVER['SERVER_PORT']	Returns the port on the server machine being used by the web server for communication (such as 80)
$_SERVER['SERVER_SIGNATURE']	Returns the server version and virtual host name which are added to server-generated pages
$_SERVER['PATH_TRANSLATED']	Returns the file system based path to the current script
$_SERVER['SCRIPT_NAME']	Returns the path of the current script
$_SERVER['SCRIPT_URI']	Returns the URI of the current page

PHP 5 while Loops

PHP while loops execute a block of code while the specified condition is true.

PHP Loops

Often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal code-lines in a script, we can use loops to perform a task like this.
In PHP, we have the following looping statements:

while - loops through a block of code as long as the specified condition is true
do...while - loops through a block of code once, and then repeats the loop as long as the specified condition is true
for - loops through a block of code a specified number of times
foreach - loops through a block of code for each element in an array

The PHP while Loop

The while loop executes a block of code as long as the specified condition is true.

Syntax

while (condition is true) {
code to be executed;
}

The example below first sets a variable $x to 1 ($x = 1). Then, the while loop will continue to run as long as $x is less than, or equal to 5 ($x <= 5). $x will increase by 1 each time the loop runs ($x++):

Example

<?php
$x = 1;

while($x <= 5) {
echo "The number is: $x ";
$x++;
}
?>

The PHP do...while Loop

The do...while loop will always execute the block of code once, it will then check the condition, and repeat the loop while the specified condition is true.

Syntax

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

The example below first sets a variable $x to 1 ($x = 1). Then, the do while loop will write some output, and then increment the variable $x with 1. Then the condition is checked (is $x less than, or equal to 5?), and the loop will continue to run as long as $x is less than, or equal to 5:

Example

<?php
$x = 1;

do {
echo "The number is: $x ";
$x++;
} while ($x <= 5);
?>

PHP 5 for Loops

PHP for loops execute a block of code a specified number of times.

The PHP for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax

for (init counter; test counter; increment counter) {
code to be executed;
}

Parameters:

init counter: Initialize the loop counter value
test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the loop continues. If it evaluates to FALSE, the loop ends.
increment counter: Increases the loop counter value

The example below displays the numbers from 0 to 10:

Example

<?php
for ($x = 0; $x <= 10; $x++) {
echo "The number is: $x ";
}
?>

The PHP foreach Loop

The foreach loop works only on arrays, and is used to loop through each key/value pair in an array.

Syntax

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

For every loop iteration, the value of the current array element is assigned to $value and the array pointer is moved by one, until it reaches the last array element.
The following example demonstrates a loop that will output the values of the given array ($colors):

Example

<?php
$colors = array("red", "green", "blue", "yellow");

foreach ($colors as $value) {
echo "$value ";
}
?>

PHP 5 switch Statement

The switch statement is used to perform different actions based on different conditions.

The PHP switch Statement

Use the switch statement to select one of many blocks of code to be executed.

Syntax

switch (n) {
    case label1:
        code to be executed if n=label1;
      break;
case label2:
      code to be executed if n=label2;
      break;
case label3:
      code to be executed if n=label3;
      break;
...
    default:
        code to be executed if n is different from all labels;
}

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.

Example

<?php
$favcolor = "red";

switch ($favcolor) {
 case "red":
 echo "Your favorite color is red!";
 break;
case "blue":
 echo "Your favorite color is blue!";
 break;
case "green":
 echo "Your favorite color is green!";
 break;
default:
 echo "Your favorite color is neither red, blue, nor green!";
}
?>

PHP 5 if...else...elseif Statements

PHP Conditional Statements

Very often when you write code, you want to perform different actions for different conditions. You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:

if statement - executes some code if one condition is true
if...else statement - executes some code if a condition is true and another code if that condition is false
if...elseif....else statement - executes different codes for more than two conditions
switch statement - selects one of many blocks of code to be executed

PHP - The if Statement

The if statement executes some code if one condition is true.

Syntax

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

The example below will output "Have a good day!" if the current time (HOUR) is less than 20:

Example

<?php
$t = date("H");

if ($t < "20") {
echo "Have a good day!";
}
?>

PHP - The if...else Statement

The if....else statement executes some code if a condition is true and another code if that condition is false.

Syntax

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

The example below will output "Have a good day!" if the current time is less than 20, and "Have a good night!" otherwise:

Example

<?php
$t = date("H");

if ($t < "20") {
echo "Have a good day!";
} else {
echo "Have a good night!";
}
?>

PHP - The if...elseif....else Statement

The if....elseif...else statement executes different codes for more than two conditions.

Syntax

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

The example below will output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":

Example

<?php
$t = date("H");

if ($t < "10") {
 echo "Have a good morning!";
} elseif ($t < "20") {
 echo "Have a good day!";
} else {
 echo "Have a good night!";
}
?>

PHP 5 Operators

PHP Operators

Operators are used to perform operations on variables and values.
PHP divides the operators in the following groups:

Arithmetic operators
Assignment operators
Comparison operators
Increment/Decrement operators
Logical operators
String operators
Array operators

PHP Arithmetic Operators

The PHP arithmetic operators are used with numeric values to perform common arithmetical operations, such as addition, subtraction, multiplication etc.

Operator	Name	Example	Result
+	Addition	$x + $y	Sum of $x and $y
-	Subtraction	$x - $y	Difference of $x and $y
*	Multiplication	$x * $y	Product of $x and $y
/	Division	$x / $y	Quotient of $x and $y
%	Modulus	$x % $y	Remainder of $x divided by $y
**	Exponentiation	$x ** $y	Result of raising $x to the $y'th power (Introduced in PHP 5.6)

PHP Assignment Operators

x = y	x = y	The left operand gets set to the value of the expression on the right
x += y	x = x + y	Addition
x -= y	x = x - y	Subtraction
x *= y	x = x * y	Multiplication
x /= y	x = x / y	Division
x %= y	x = x % y	Modulus

PHP Comparison Operators

Operator	Name	Example	Result
==	Equal	$x == $y	Returns true if $x is equal to $y
===	Identical	$x === $y	Returns true if $x is equal to $y, and they are of the same type
!=	Not equal	$x != $y	Returns true if $x is not equal to $y
<>	Not equal	$x <> $y	Returns true if $x is not equal to $y
!==	Not identical	$x !== $y	Returns true if $x is not equal to $y, or they are not of the same type
>	Greater than	$x > $y	Returns true if $x is greater than $y
<	Less than	$x < $y	Returns true if $x is less than $y
>=	Greater than or equal to	$x >= $y	Returns true if $x is greater than or equal to $y
<=	Less than or equal to	$x <= $y	Returns true if $x is less than or equal to $y

PHP Increment / Decrement Operators

++$x	Pre-increment	Increments $x by one, then returns $x
$x++	Post-increment	Returns $x, then increments $x by one
--$x	Pre-decrement	Decrements $x by one, then returns $x
$x--	Post-decrement	Returns $x, then decrements $x by one

PHP Logical Operators

and	And	$x and $y	True if both $x and $y are true
or	Or	$x or $y	True if either $x or $y is true
xor	Xor	$x xor $y	True if either $x or $y is true, but not both
&&	And	$x && $y	True if both $x and $y are true
\|\|	Or	$x \|\| $y	True if either $x or $y is true
!	Not	!$x	True if $x is not true

PHP String Operators

Operator	Name	Example	Result
.	Concatenation	$txt1 . $txt2	Concatenation of $txt1 and $txt2
.=	Concatenation assignment	$txt1 .= $txt2	Appends $txt2 to $txt1

PHP Array Operators

Operator	Name	Example	Result
+	Union	$x + $y	Union of $x and $y
==	Equality	$x == $y	Returns true if $x and $y have the same key/value pairs
===	Identity	$x === $y	Returns true if $x and $y have the same key/value pairs in the same order and of the same types
!=	Inequality	$x != $y	Returns true if $x is not equal to $y
<>	Inequality	$x <> $y	Returns true if $x is not equal to $y
!==	Non-identity	$x !== $y	Returns true if $x is not identical to $y

PHP 5 Constants

Constants are like variables except that once they are defined they cannot be changed or undefined.

PHP Constants

A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
A valid constant name starts with a letter or underscore (no $ sign before the constant name).
Note: Unlike variables, constants are automatically global across the entire script.

Create a PHP Constant

To create a constant, use the define() function.

Syntax

define(name, value, case-insensitive)

Parameters:

name: Specifies the name of the constant
value: Specifies the value of the constant
case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false

The example below creates a constant with a case-sensitive name:

Example

<?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>

Constants are Global

Constants are automatically global and can be used across the entire script.
The example below uses a constant inside a function, even if it is defined outside the function:

Example

<?php
define("GREETING", "Welcome to W3Schools.com!");

function myTest() {
echo GREETING;
}

myTest();
?>