PHP – Minimal Guide for Beginners

PHP is a general-purpose scripting language especially suited for Web development. It is open-source and can be deployed on all major operating systems and web servers free of charge. It is imperative, reflective and supports object-oriented programming.

Basic Syntax

Similarities with other imperative languages PHP code should look familiar to anyone who has had experience with C, C++ or Java. Statements are terminated with a “;” and blocks of code are delimited with “{” and “}“. The “/*…*/” and “//” notations are both valid for PHP. Control structures such as if-else statements , for loops and while loops work in much the same way as with the above mentioned languages.

Read More: PHP Error Reporting Minimal Guide

However, there are some differences and features that are unique to PHP which will be briefly explored in the rest of this article.

Variables

Variables in PHP are represented by a “$” character followed by the name of the variable . For example , the variable “foobar” would be re presented as “$foobar” in PHP code. Variable names in PHP are case-sensitive and m us t s tart with either an underscore or a letter, followed by any number of letters , numbers or underscores .

The following code stub demonstrates the assignment of a value to a variable .

$foo = ‘bar’;

Note that PHP does not by default enforce the declaration of a variable before its usage , so some care should be taken not to attempt to access the value of a variable before one has been assigned to it.

Escaping HTML

PHP code can embedded with in HTML using the “<?php” and “?>” tags . For example , the following code would output “Hello, foobar!“.

<html>
<body>
<?php $lastname = “bar”; ?>
Hello, foo<?php echo $lastname; ?>!
</body>
</html>

Types

PHP supports the following eight primitive data types.

four scalar types: boolean, integer, float, string
two compound types: array, object
two special types: resource , NULL

PHP is a weakly-typed language. This means that the programmer is usually not required to resolve the type of a variable. Instead, the type of a variable is usually resolved during runtime depending on the context in which it is being used. This can sometimes be tricky, as we shall see.

Booleans

The boolean type can take the values true or false. Since PHP is weakly-typed, variables of other types can be implicitly cast as booleans. How ever, one must be careful when doing this, because some values of other types are evaluated to FALSE, as listed below.

the integer 0 and the float 0.0
the string “0” and empty strings
an array with zero elements
an object with zero member variables (PHP 4 only)
the NULL special type

Integers and floats

Integers can be specified in decimal (10-based), hexadecimal (16-based) or octal (8-based) notation, optionally preceded by a sign (– or + ). Octal numbers are preceded by 0 and hexadecimals are preceded by 0x. Floating point numbers can be specified in any of the following three formats.

$a = 1.234;
$b = 1.2e3;
$c = 7E-10;

Strings

A string in PHP can be specified with single quotes, double quotes or the here doc syntax. Since this is a just a article, the here doc syntax will not be covered for the sake of brevity.

The simplest way to specify a string is to delimit it with single quotes . To specify a single quote with in a single-quoted string, it needs to be preceded by a backslash (\). If a backslash is to occur before a single quote , then a double back slash is required. Otherwise , there is normally no need to escape backslashes .

For example, the code below would print “This is a back slash \, a single quote ‘ and a backslash followed by a single quote \'”.

echo ‘This is a backslash \, a single quote \’ and a backslash followed by a single quote \\”;

For double-quoted strings in PHP, more of the escape sequences found in other languages may be used, such as “\n”, “\t” and “\r”. However, the most important feature of double-quoted strings in PHP is that variables are expanded.

For example, the code below would print “Variable $foo has a value of bar“.

$foo = ‘ba’.’r’; //’.’ is the concatenation operator
echo “Variable \$foo has a value of $foo”;

Arrays

It is beyond the scope of this article to fully describe the PHP array type , so only a brief summary will be given. An array in PHP is an ordered map. A map is a type that maps values to keys. An array in PHP may be created using the array() function, as shown below.

$arr=array(“key1″=>”val1″,”key2″=>”val2″,”val3”);

The above statement would result in an array with the elements val1, val2 and val3. Since the key of val3 was not specified, it would take the value 0, the smallest available non-negative integer. Alternatively, the above array could have been specified using the following syntax.

$arr[‘key1’] = ‘val1’; //$arr is created
$arr[‘key2’] = ‘val2’;
$arr[] = ‘val3’; //$arr[0] is equivalent

Legal values for keys of arrays are any values of primitive types , with boolean true and false being cast as 1 and 0 respectively. Floating point numbers used as keys are truncated and NULL is cast as an empty string. An empty string, of course , remains an empty string.

Objects

Objects in PHP, like arrays , is a very wide topic and hence will not be covered beyond basic class declaration and object instantiation syntax.

//class Declaration
class className [extends parentClassname] {
var $attribute;
//constructor
function className([$params]){statement;}
//member function
function functionName([$params]){statements;}
}
//class instantiation
$ob = new className();
//calling a member function
$result = $ob->functionName();

Type functions

Some useful functions for dealing with types are the var_dump(), gettype() and is _* functions. The var_dump function recursively dumps the entire variable passed in, including the types of the variable and all its members (for objects) and elements (for arrays). The gettype function returns
the type of the variable passed in and the is _* functions test if a variable is of a certain type .

For more information about PHP data types , please refer to “http://php.net/manual/en/language.types.php“.

Post, Get, Session and Databases

Since PHP is most commonly used to program web applications , it requires ways to obtain data from the user through HTTP POST and GET methods as well as ways to maintain coherent sessions for users . Finally, most web applications require ways to store user-submitted data.

Useful Superglobals

All POST variables may be obtained from an array called $_POST and all GET variables from the $_GET array. These variables are called superglobal variables, which means that they are automatically global. PHP provides a few other useful superglobals, including $_COOKIE for cookies and $_FILES for uploaded files .

Session Handling

To start a session, the session_start() function must be called before any other output is sent to the browser, after which the $_SESSION superglobal may be used to store all session variables. Subsequently, all pages that form a part of the session must also call the session_start() function. To end a session, the session_destroy() function is called.

Handling Databases

PHP has libraries for interfacing with most of the popular relational database servers in use today. These include MySQL, PostgreSQL, Oracle and MSSQL. It is beyond the scope of this article to exhaustively explore the rich libraries of functions provided by PHP to access these databases.

However, one of the most useful features about PHP is that it tries to provide a more or less consistent suite of similarly named functions that are valid for most databases. For instance, to connect to a database server, one would use a *_connect() function, where * is replaced by the type of server.

For a MySQL server, one would use mysql_connect(), for a MSSQL server, one would use mssql_connect() and so on. The functions used to query databases are not so consistently named, but after a query has been executed, one would use the *_fetch_assoc(), *_fetch_array() and *_fetch_row() functions to retrieve the data from the queries. Finally, to close the connection to the database , one would call the *_close() function.

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