Chapter
4:-Introduction to PHP
Characteristics Of PHP
Familiarity: -
If
you are in programming background then you can easily understand the PHP
syntax. And you can write PHP script because of most of PHP syntax inherited
from other languages like C or Pascal.
Simplicity: -
PHP
provides a lot of pre-define functions to secure your data. It is also
compatible with many third-party applications, and PHP can easily integrate
with other.
In
PHP script there is no need to include libraries like c, special compilation
directives like Java, PHP engine starts execution from (<?) escape sequence
and end with a closing escape sequence (<?). In PHP script, there is no need
to write main function. And also you can work with PHP without creating a
class.
Efficiency: -
PHP
4.0 introduced resource allocation mechanisms and more pronounced support for
object-oriented programming, in addition to session management features.
Eliminating unnecessary memory allocation.
Security: -
Several
trusted data encryption options are supported in PHP’s predefined function set.
You can use a lot of third-party applications to secure our data, allowing for
securing our application.
Flexibility: -
You
can say that PHP is a very flexible language because of PHP is an embedded
language you can embed PHP scripts with HTML, JAVA SCRIPT, WML, XML, and many
others. You can run your PHP script any device like mobile Phone, tabs,
laptops, PC and other because of PHP script execute on the server then after
sending to the browser of your device.
Free: -
PHP
is an open source programming language so you can download freely there is no
need to buy a licence or anything.
Object Oriented: -
PHP
has added some object-oriented programming features, and Object Oriented
programming became possible with PHP 4. With the introduction of PHP 5, the PHP
developers have really beefed up the object-oriented features of PHP, resulting
in both more speed and added features.
PHP lexical structure
Computer languages, like human
languages, have a lexical structure. A source code of a PHP script consists of
tokens. Tokens are atomic code elements. In PHP language, we have comments,
variables, literals, operators, delimiters, and keywords.
PHP comments
Comments are used by humans to clarify
the source code. All comments in PHP follow the #character.
<?php
# ZetCode 2016
echo "This is comments.php
script\n";
?>
Single line comment
// comments.php
// author Jan Bodnar
// ZetCode 2016
Multiline comment
/*
comments.php
author Jan Bodnar
ZetCode 2016
*/
PHP semicolon
A semicolon is used to mark the end of a
statement in PHP. It is mandatory.
$a = 34;
$b = $a * 34 - 34;
echo $a;
The variables are case sensitive. This
means that $Price, $price, and $PRICE are three different identifiers.
<?php
$number = 10;
$Number = 11;
$NUMBER = 12;
echo $number, $Number, $NUMBER;
echo "\n";
?>
PHP constants
A constant is an identifier for a value
which cannot change during the execution of the script. By convention, constant
identifiers are always uppercase.
<?php
define("SIZE", 300);
define("EDGE", 100);
#SIZE = 100;
echo SIZE;
echo EDGE;
echo "\n";
?>
PHP Data Types
Variables can store data of
different types, and different data types can do different things.
PHP supports the following data
types:
PHP String
A string is a sequence of
characters, like "Hello world!".
<html>
<body>
<?php
$x = "Hello world!";
$y = 'Hello world!';
echo $x;
echo "<br>";
echo $y;
?>
</body>
</html>
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)
<html>
<body>
<?php
$x = 5985;
var_dump($x);
?>
</body>
</html>
int(5985)
PHP Float
A float (floating point number) is a
number with a decimal point or a number in exponential form.
<html>
<body>
<?php
$x = 10.365;
var_dump($x);
?>
</body>
</html>
Float(10.365)
PHP Boolean
A Boolean represents two possible
states: TRUE or FALSE.
$x = true;
$y = false;
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:
<html>
<body>
<?php
$cars =
array("Volvo","BMW","Toyota");
var_dump($cars);
?>
</body>
</html>
array(3) { [0]=> string(5)
"Volvo" [1]=> string(3) "BMW" [2]=> string(6)
"Toyota" }
PHP
Variables
A
variable in PHP is a name of memory location that holds data. A variable is a
temporary storage that is used to store data temporarily.
In
PHP, a variable is declared using $ sign followed by variable name.
PHP
Variable: Declaring string, integer and float
<?php
$str="hello
string";
$x=200;
$y=44.6;
echo
"string is: $str <br/>";
echo
"integer is: $x <br/>";
echo
"float is: $y <br/>";
?>
Output:
string
is: hello string
integer
is: 200
float
is: 44.6
Sum
of two variables
<?php
$x=5;
$y=6;
$z=$x+$y;
echo
$z;
?>
case
sensitive
In
PHP, variable names are case sensitive. So variable name "color" is
different from Color, COLOR, COLor etc.
<?php
$color="red";
echo
"My car is " . $color . "<br>";
echo
"My house is " . $COLOR . "<br>";
echo
"My boat is " . $coLOR . "<br>";
?>
PHP
Variable: Rules
PHP
variables must start with letter or underscore only.
PHP
variable can't be start with numbers and special symbols.
<?php
$a="hello";//letter
(valid)
$_b="hello";//underscore
(valid)
echo
"$a <br/> $_b";
?>
PHP $ and $$ Variables
The
$var (single dollar) is a normal variable with the name var that stores any
value like string, integer, float, etc.
The
$$var (double dollar) is a reference variable that stores the value of the
$variable inside it.
<?php
$x
= "abc";
$$x
= 200;
echo
$x."<br/>";
echo
$$x."<br/>";
echo
$abc;
?>
abc
200
200
Typecasting
IN PHP:
The
meaning of type casting is to use the value of a variable with different data
type. In other word typecasting is a way to utilize one data type variable into
the different data type.
We
can cast following data type variable in PHP
•(int),
(integer) - cast to integer
•(bool),
(boolean) - cast to boolean
•(float),
(double), (real) - cast to float
•(string)
- cast to string
•(array)
- cast to array
•(object)
- cast to object
Example
(int)
operator changes type to Integer
(float)
operator changes type to Float
Example:-
$a=”5”;
$b=(int)$a;
$a=(int)$a;
Type
juggling
Php
variables can store integers,floating point,strings and more.
The
conversion of a value from one type to another is called casting.This kind of implicit casting is
called type juggling in php.
Type
of first operand is Integer and Type of second operator Floating point
Result
is The integer is converted to a floating point.
Type
of first operand is Integer and Type of second operator String
Result
is String is converted to a integer
Type
of first operand is Floating point and Type of second operator String
Result
is The string is converted to a floating point.
<?php
$x=”3.14
pies”*2;
echo”$x=$x”;
?>
$x=6.28
Control
structure
PHP
If Statement
PHP
if statement is executed if condition is true.
Syntax
if(condition){
//code
to be executed
}
<?php
$num=12;
if($num<100){
echo
"$num is less than 100";
}
?>
Output:
12
is less than 100
PHP
If-else Statement
PHP
if-else statement is executed whether condition is true or false.
Syntax
if(condition){
//code
to be executed if true
}else{
//code
to be executed if false
}
<?php
$num=12;
if($num%2==0)
{
echo
"$num is even number";
}else{
echo
"$num is odd number";
}
?>
Output:
12
is even number
PHP
Switch
PHP
switch statement is used to execute one statement from multiple conditions. It
works like PHP if-else-if statement.
Syntax
switch(expression){
case
value1:
//code to be executed
break;
case
value2:
//code to be executed
break;
......
default:
code to be executed if all cases are not
matched;
}
<?php
$num=20;
switch($num)
{
case
10:
echo("number
is equals to 10");
break;
case
20:
echo("number
is equal to 20");
break;
case
30:
echo("number
is equal to 30");
break;
default:
echo("number
is not equal to 10, 20 or 30");
}
?>
Output:
number
is equal to 20
PHP
For Loop
PHP
for loop can be used to traverse set of code for the specified number of times.
It
should be used if number of iteration is known otherwise use while loop.
for(initialization;
condition; increment/decrement){
//code
to be executed
}
<?php
for($n=1;$n<=10;$n++)
{
echo
"$n<br/>";
}
?>
1
2 3 4 5 6 7 8 9 10
PHP
While Loop
PHP
while loop can be used to traverse set of code like for loop.
It
should be used if number of iteration is not known.
while(condition)
{
//code
to be executed
}
<?php
$n=1;
while($n<=10)
{
echo
"$n<br/>";
$n++;
}
?>
1
2 3 4 5 6 7 8 9 10
PHP
do while loop
PHP
do while loop can be used to traverse set of code like php while loop. The PHP
do-while loop is guaranteed to run at least once.
It
executes the code at least one time always because condition is checked after
executing the code.
do
{
//code
to be executed
}while(condition);
<?php
$n=1;
do
{
echo
"$n<br/>";
$n++;
}while($n<=10);
?>
1
2 3 4 5 6 7 8 9 10
GET vs. POST
Both GET and POST create
an array (e.g. array( key1 => value1, key2 => value2, key3 => value3,
...)). This array holds key/value pairs, where keys are the names of the form
controls and values are the input data from the user.
Both GET and POST are
treated as $_GET and $_POST. These 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.
$_GET is an array of
variables passed to the current script via the URL parameters.
$_POST is an array of
variables passed to the current script via the HTTP POST method.
When to use GET?
Information sent from a
form with the GET method is visible to everyone (all variable names and values
are displayed in the URL). GET also has limits on the amount of information to
send. The limitation is about 2000 characters. However, because the variables
are displayed in the URL, it is possible to bookmark the page. This can be
useful in some cases.
GET may be used for
sending non-sensitive data.
<html>
<body>
<form
action="welcome_get.php" method="get">
Name: <input
type="text" name="name"><br>
E-mail: <input
type="text" name="email"><br>
<input
type="submit">
</form>
</body>
</html>
welcome_get.php
<html>
<body>
Welcome <?php echo
$_GET["name"]; ?><br>
Your email address is:
<?php echo $_GET["email"]; ?>
</body>
</html>
When to use POST?
Information sent from a
form with the POST method is invisible to others (all names/values are embedded
within the body of the HTTP request) and has no limits on the amount of
information to send.
Moreover POST supports
advanced functionality such as support for multi-part binary input while
uploading files to server.
However, because the
variables are not displayed in the URL, it is not possible to bookmark the
page.
<html>
<body>
<form
action="welcome.php" method="post">
Name: <input
type="text" name="name"><br>
E-mail: <input
type="text" name="email"><br>
<input
type="submit">
</form>
</body>
</html>
welcome.php
<html>
<body>
Welcome <?php echo
$_POST["name"]; ?><br>
Your email address is:
<?php echo $_POST["email"]; ?>
</body>
</html>
PHP: $_REQUEST
$_REQUEST is a super
global variable which is widely used to collect data after submitting html
forms
The PHP built-in
$_REQUEST function can be used with both the GET and POST methods
<html>
<body>
<form
action="test.php" method="post">
Your name: <input
type="text" name="yourname" />
<input
type="submit" />
</form>
</body>
</html>
test.php
Welcome <?php echo
$_REQUEST ["yourname"]; ?>
PHP Echo
PHP echo is a language
construct not a function, so you don't need to use parenthesis with it. But if
you want to use more than one parameters, it is required to use parenthesis.
<?php
echo "Hello by PHP
echo";
?>
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.
<html>
<body>
<?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.";
?>
</body>
</html>
PHP is Fun!
Hello world!
I'm about to learn PHP!
This string was made
with multiple parameters
<html>
<body>
<?php
print
"<h2>PHP is Fun!</h2>";
print "Hello
world!<br>";
print "I'm about to
learn PHP!";
?>
</body>
</html>
PHP is Fun!
Hello world!
I'm about to learn PHP!
