w3schoolworld: October 2016

Sunday, 9 October 2016

PHP String Functions

PHP String Functions
In this chapter we will look at some commonly used functions to manipulate strings.

Get The Length of a String
The PHP strlen() function returns the length of a string.

The example below returns the length of the string "Hello w3schoolworld!":

Example
<?php
echo strlen("Hello w3schoolworld!"); // outputs 20
?>

The output of the code above will be: 20.

Count The Number of Words in a String
The PHP str_word_count() function counts the number of words in a string:

Example
<?php
echo str_word_count("Hello w3schoolworld!"); // outputs 2
?>

The output of the code above will be: 2.

Reverse a String
The PHP strrev() function reverses a string:

Example
<?php
echo strrev("Hello world!"); // outputs !dlrow olleH
?>

The output of the code above will be: !dlrow olleH.

Search For a Specific Text Within a String
The PHP strpos() function searches for a specific text within a string.

If a match is found, the function returns the character position of the first match. If no match is found, it will return FALSE.

The example below searches for the text "world" in the string "Hello world"

Example

<?php
echo strpos("Hello world!", "world"); // outputs 6
?>

The output of the code above will be: 6.

Tip: The first character position in a string is 0 (not 1).

Replace Text Within a String
The PHP str_replace() function replaces some characters with some other characters in a string.

The example below replaces the text "world" with "Dolly":

Example
<?php
echo str_replace("world", "Dolly", "Hello world!"); // outputs Hello Dolly!
?>

The output of the code above will be: Hello Dolly!

Complete PHP String Reference
For a complete reference of all string functions, go to our complete PHP String Reference.

The PHP string reference contains description and example of use, for each function!

PHP Data Types

PHP Data Types
Variables can store data of different types, and different data types can do different things.

PHP supports the following data types:

String
Integer
Float (floating point numbers - also called double)
Boolean
Array
Object
NULL
Resource
PHP String
A string is a sequence of characters, like "Hello world!".

A string can be any text inside quotes. You can use single or double quotes:

Example
<?php
$x = "Hello world!";
$y = 'Hello world!';

echo $x;
echo "<br>";
echo $y;
?>

PHP Integer
An integer data type is a non-decimal number between -2,147,483,648 and 2,147,483,647.

Rules for integers:

An integer must have at least one digit
An integer must not have a decimal point
An integer can be either positive or negative
Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based - prefixed with 0x) or octal (8-based - prefixed with 0)
In the following example $x is an integer. The PHP var_dump() function returns the data type and value:

Example
<?php
$x = 5985;
var_dump($x);
?>

PHP Float
A float (floating point number) is a number with a decimal point or a number in exponential form.

In the following example $x is a float. The PHP var_dump() function returns the data type and value:

Example
<?php
$x = 10.365;
var_dump($x);
?>

PHP Boolean
A Boolean represents two possible states: TRUE or FALSE.

$x = true;
$y = false;
Booleans are often used in conditional testing. You will learn more about conditional testing in a later chapter of this tutorial.

PHP Array
An array stores multiple values in one single variable.

In the following example $cars is an array. The PHP var_dump() function returns the data type and value:

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

You will learn a lot more about arrays in later chapters of this tutorial.

PHP Object
An object is a data type which stores data and information on how to process that data.

In PHP, an object must be explicitly declared.

First we must declare a class of object. For this, we use the class keyword. A class is a structure that can contain properties and methods:

Example
<?php
class Car {
    function Car() {
        $this->model = "VW";
    }
}

// create an object
$herbie = new Car();

// show object properties
echo $herbie->model;
?>

You will learn more about objects in a later chapter of this tutorial.

PHP NULL Value
Null is a special data type which can have only one value: NULL.

A variable of data type NULL is a variable that has no value assigned to it.

Tip: If a variable is created without a value, it is automatically assigned a value of NULL.

Variables can also be emptied by setting the value to NULL:

Example
<?php
$x = "Hello world!";
$x = null;
var_dump($x);
?>

PHP Resource
The special resource type is not an actual data type. It is the storing of a reference to functions and resources external to PHP.

A common example of using the resource data type is a database call.

We will not talk about the resource type here, since it is an advanced topic.

how use PHP 5 echo and print Statements

PHP 5 echo and print Statements

In PHP there are two basic ways to get output: echo and print.

In this tutorial we use echo (and print) in almost every example. So, this chapter contains a little more info about those two output statements.

PHP echo and print Statements
echo and print are more or less the same. They are both used to output data to the screen.

The differences are small: echo has no return value while print has a return value of 1 so it can be used in expressions. echo can take multiple parameters (although such usage is rare) while print can take one argument. echo is marginally faster than print.

The PHP echo Statement
The echo statement can be used with or without parentheses: echo or echo().

Display Text

The following example shows how to output text with the echo command (notice that the text can contain HTML markup):

Example
<?php
echo "<h2>PHP is Fun!</h2>";
echo "Hello world!<br>";
echo "I'm about to learn PHP!<br>";
echo "This ", "string ", "was ", "made ", "with multiple parameters.";
?>

Display Variables

The following example shows how to output text and variables with the echo statement:

Example
<?php
$txt1 = "Learn PHP";
$txt2 = "W3Schoolworld.com";
$x = 5;
$y = 4;

echo "<h2>$txt1</h2>";
echo "Study PHP at $txt2<br>";
echo $x + $y;
?>

The PHP print Statement
The print statement can be used with or without parentheses: print or print().

Display Text

The following example shows how to output text with the print command (notice that the text can contain HTML markup):

Example
<?php
print "<h2>PHP is Fun!</h2>";
print "Hello world!<br>";
print "I'm about to learn PHP!";
?>

Display Variables

The following example shows how to output text and variables with the print statement:

Example
<?php
$txt1 = "Learn PHP";
$txt2 = "W3Schoolworld.com";
$x = 5;
$y = 4;

print "<h2>$txt1</h2>";
print "Study PHP at $txt2<br>";
print $x + $y;
?>

Creating (Declaring) PHP Variables

Creating (Declaring) PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

Example
<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;
?>

PHP Variables
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).

Rules for PHP variables:

A variable starts with the $ sign, followed by the name of the variable
A variable name must start with a letter or the underscore character
A variable name cannot start with a number
A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
Variable names are case-sensitive ($age and $AGE are two different variables)
Remember that PHP variable names are case-sensitive!

Output Variables
The PHP echo statement is often used to output data to the screen.

The following example will show how to output text and a variable:

Example
<?php
$txt = "W3Schoolworld.com";
echo "I love $txt!";
?>

The following example will produce the same output as the example above:

Example
<?php
$txt = "W3Schoolworld.com";
echo "I love " . $txt . "!";
?>

The following example will output the sum of two variables:

Example
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>

Note: You will learn more about the echo statement and how to output data to the screen in the next chapter.

PHP is a Loosely Typed Language
In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on its value.

In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.

PHP Variables Scope
In PHP, variables can be declared anywhere in the script.

The scope of a variable is the part of the script where the variable can be referenced/used.

PHP has three different variable scopes:

local
global
static

Global and Local Scope
A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:

Example
<?php
$x = 5; // global scope

function myTest() {
// using x inside this function will generate an error
echo "<p>Variable x inside function is: $x</p>";
}
myTest();

echo "<p>Variable x outside function is: $x</p>";
?>

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:

Example
<?php
function myTest() {
$x = 5; // local scope
echo "<p>Variable x inside function is: $x</p>";
}
myTest();

// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>

You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.

PHP The global Keyword
The global keyword is used to access a global variable from within a function.

To do this, use the global keyword before the variables (inside the function):

Example
<?php
$x = 5;
$y = 10;

function myTest() {
global $x, $y;
$y = $x + $y;
}

myTest();
echo $y; // outputs 15
?>

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.

The example above can be rewritten like this:

Example
<?php
$x = 5;
$y = 10;

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

myTest();
echo $y; // outputs 15
?>

PHP The static Keyword
Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job.

To do this, use the static keyword when you first declare the variable:

Example
<?php
function myTest() {
    static $x = 0;
    echo $x;
    $x++;
}

myTest();
myTest();
myTest();
?>

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.

Note: The variable is still local to the function.

Creating (Declaring) PHP Variables

Creating (Declaring) PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

Example
<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;
?>

PHP Variables
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).

Rules for PHP variables:

Output Variables
The PHP echo statement is often used to output data to the screen.

The following example will show how to output text and a variable:

Example
<?php
$txt = "W3Schoolworld.com";
echo "I love $txt!";
?>

The following example will produce the same output as the example above:

Example
<?php
$txt = "W3Schoolworld.com";
echo "I love " . $txt . "!";
?>

The following example will output the sum of two variables:

Example
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>

Note: You will learn more about the echo statement and how to output data to the screen in the next chapter.

PHP is a Loosely Typed Language
In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on its value.

In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.

PHP Variables Scope
In PHP, variables can be declared anywhere in the script.

The scope of a variable is the part of the script where the variable can be referenced/used.

PHP has three different variable scopes:

local
global
static

Global and Local Scope
A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:

Example
<?php
$x = 5; // global scope

function myTest() {
// using x inside this function will generate an error
echo "<p>Variable x inside function is: $x</p>";
}
myTest();

echo "<p>Variable x outside function is: $x</p>";
?>

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:

Example
<?php
function myTest() {
$x = 5; // local scope
echo "<p>Variable x inside function is: $x</p>";
}
myTest();

// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>

You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.

PHP The global Keyword
The global keyword is used to access a global variable from within a function.

To do this, use the global keyword before the variables (inside the function):

Example
<?php
$x = 5;
$y = 10;

function myTest() {
global $x, $y;
$y = $x + $y;
}

myTest();
echo $y; // outputs 15
?>

The example above can be rewritten like this:

Example
<?php
$x = 5;
$y = 10;

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

myTest();
echo $y; // outputs 15
?>

PHP The static Keyword
Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job.

To do this, use the static keyword when you first declare the variable:

Example
<?php
function myTest() {
    static $x = 0;
    echo $x;
    $x++;
}

myTest();
myTest();
myTest();
?>

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.

Note: The variable is still local to the function.

how use Comments in PHP

Comments in PHP
A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is looking at the code.

Comments can be used to:

Let others understand what you are doing
Remind yourself of what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code
PHP supports several ways of commenting:

Example
<!DOCTYPE html>
<html>
<body>

<?php
// This is a single-line comment

# This is also a single-line comment

/*
This is a multiple-lines comment block
that spans over multiple
lines
*/

// You can also use comments to leave out parts of a code line
$x = 5 /* + 15 */ + 5;
echo $x;
?>

</body>
</html>

PHP Case Sensitivity
In PHP, all keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are NOT case-sensitive.

In the example below, all three echo statements below are legal (and equal):

Example
<!DOCTYPE html>
<html>
<body>

<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>

</body>
</html>

However; all variable names are case-sensitive.

In the example below, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are treated as three different variables):

Example
<!DOCTYPE html>
<html>
<body>

<?php
$color = "red";
echo "My car is " . $color . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>

</body>
</html>

Basic PHP Syntax

A PHP script is executed on the server, and the plain HTML result is sent back to the browser.

Basic PHP Syntax
A PHP script can be placed anywhere in the document.

A PHP script starts with <?php and ends with ?>:

<?php
// PHP code goes here
?>
The default file extension for PHP files is ".php".

A PHP file normally contains HTML tags, and some PHP scripting code.

Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page:

Example
<!DOCTYPE html>
<html>
<body>

<h1>My first PHP page example</h1>

<?php
echo "Hello w3schoolWorld!";
?>

</body>
</html>

PHP 5 how Install??

What Do I Need?
To start using PHP, you can:

Find a web host with PHP and MySQL support
Install a web server on your own PC, and then install PHP and MySQL
Use a Web Host With PHP Support
If your server has activated support for PHP you do not need to do anything.

Just create some .php files, place them in your web directory, and the server will automatically parse them for you.

You do not need to compile anything or install any extra tools.

Because PHP is free, most web hosts offer PHP support.

Set Up PHP on Your Own PC
However, if your server does not support PHP, you must:

install a web server
install PHP
install a database, such as MySQL
The official PHP website (PHP.net) has installation instructions for PHP: http://php.net/manual/en/install.php