PHP tutorial : PHP 5 - Syntax, Variables Function in detail - part 1
PHP 5 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</h1>
<?php
echo "Hello World!";
?>
</body>
</html>
Note: PHP statements end with a semicolon (;).
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>
___________________________________________________
PHP 5 Variables
Variables are "containers" for storing information.
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;
?>
After the execution of the statements above, the variable $txt will hold the value Hello world!, the variable $x will hold the value 5, and the variable $y will hold the value 10.5.
Note: When you assign a text value to a variable, put quotes around the value.
Note: Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.
Think of variables as containers for storing data.
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 = "W3Schools.com";
echo "I love $txt!";
?>
The following example will produce the same output as the example above:
Example
<?php
$txt = "W3Schools.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.
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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 = "W3Schools.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 = "W3Schools.com";
$x = 5;
$y = 4;
print "<h2>$txt1</h2>";
print "Study PHP at $txt2<br>";
print $x + $y;
?>
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PHP 5 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.
___________________________________________________
PHP 5 Strings
A string is a sequence of characters, like "Hello world!".
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 world!":
Example
<?php
echo strlen("Hello world!"); // outputs 12
?>
The output of the code above will be: 12.
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 world!"); // 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!
___________________________________________________
<!DOCTYPE html>
<html>
<body>
<?php
echo strlen("Hello world!");
?>
</body>
</html>
*********** 12
___________________________________________________
<!DOCTYPE html>
<html>
<body>
<?php
echo str_word_count("Hello world!");
?>
</body>
</html>
*********** 2
___________________________________________________
<!DOCTYPE html>
<html>
<body>
<?php
echo strrev("Hello world!");
?>
</body>
</html>
*********** !dlrow olleH
___________________________________________________
<!DOCTYPE html>
<html>
<body>
<?php
echo strpos("Hello world!", "world");
?>
</body>
</html>
*********** 6
___________________________________________________
<!DOCTYPE html>
<html>
<body>
<?php
echo str_replace("world", "Dolly", "Hello world!");
?>
</body>
</html>
*********** Hello Dolly!
___________________________________________________
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;
?>
The example below creates a constant with a case-insensitive name:
Example
<?php
define("GREETING", "Welcome to W3Schools.com!", true);
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();
?>
___________________________________________________
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 Show it
+ 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
The PHP assignment operators are used with numeric values to write a value to a variable.
The basic assignment operator in PHP is "=". It means that the left operand gets set to the value of the assignment expression on the right.
Assignment Same as... Description Show it
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
The PHP comparison operators are used to compare two values (number or string):
Operator Name Example Result Show it
== 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 $y
PHP Increment / Decrement Operators
The PHP increment operators are used to increment a variable's value.
The PHP decrement operators are used to decrement a variable's value.
Operator Name Description Show it
++$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
The PHP logical operators are used to combine conditional statements.
Operator Name Example Result Show it
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
PHP has two operators that are specially designed for strings.
Operator Name Example Result Show it
. Concatenation $txt1 . $txt2 Concatenation of $txt1 and $txt2
.= Concatenation assignment $txt1 .= $txt2 Appends $txt2 to $txt1
PHP Array Operators
The PHP array operators are used to compare arrays.
Operator Name Example Result Show it
+ 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
___________________________________________________
Arithmetic operator: Addition (+)
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
$y = 6;
echo $x + $y;
?>
</body>
</html>
*********** 16
___________________________________________________
Arithmetic operator: Subtraction (-)
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
$y = 6;
echo $x - $y;
?>
</body>
</html>
*********** 4
___________________________________________________
Arithmetic operator: Multiplication (*)
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
$y = 6;
echo $x * $y;
?>
</body>
</html>
*********** 60
___________________________________________________
Arithmetic operator: Division (/)
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
$y = 6;
echo $x / $y;
?>
</body>
</html>
*********** 1.6666666666667
___________________________________________________
Arithmetic operator: Modulus (%)
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
$y = 6;
echo $x % $y;
?>
</body>
</html>
*********** 4
___________________________________________________
Assignment operator: x = y
<!DOCTYPE html>
<html>
<body>
<?php
$x = 10;
echo $x;
?>
</body>
</html>
*********** 10
___________________________________________________
Assignment operator: x += y
<!DOCTYPE html>
<html>
<body>
<?php
$x = 20;
$x += 100;
echo $x;
?>
</body>
</html>
*********** 120
___________________________________________________
Assignment operator: x -= y
<!DOCTYPE html>
<html>
<body>
<?php
$x = 50;
$x -= 30;
echo $x;
?>
</body>
</html>
*********** 20
___________________________________________________
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