PHP/Variables - Revision history

wikademia>Wikademia: moved Variables in PHP to PHP/Variables

2009-06-13T06:12:41Z

← Older revision	Revision as of 06:12, 13 June 2009
(No difference)

wikademia>Wikademia: Text replace - '[[Topic:' to '[['

2009-06-08T04:00:43Z

Text replace - '[[Topic:' to '[['

← Older revision		Revision as of 04:00, 8 June 2009
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	== Declaration ==		== Declaration ==
	In a more lower-level language like [[~~Topic:~~C++\|C++]], the declaration of the type of each variable is needed. For example, the following code in PHP:		In a more lower-level language like [[C++\|C++]], the declaration of the type of each variable is needed. For example, the following code in PHP:
	<source lang="php">		<source lang="php">
	<?php		<?php
Line 58:		Line 58:
	</source>		</source>

	Does not explicitly define the type of variable ''a''. Of course, the PHP runtime environment recognizes during execution of this line that the programmer provided a string literal as the value for the variable. If you want to do the same in [[~~Topic:~~C++\|C++]], you would would have to explicitly declare the variable type:		Does not explicitly define the type of variable ''a''. Of course, the PHP runtime environment recognizes during execution of this line that the programmer provided a string literal as the value for the variable. If you want to do the same in [[C++\|C++]], you would would have to explicitly declare the variable type:
	<source lang="php">		<source lang="php">
	char[6] a;		char[6] a;

wikademia>Wikademia at 21:31, 12 April 2009

2009-04-12T21:31:17Z

← Older revision		Revision as of 21:31, 12 April 2009
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	Variables, as mentioned briefly in [[Introduction to PHP]], are a significant feature of any programming language. They can be used to store all forms of data, and are generally required to perform multiple manipulations on data not hard-coded into a script. This lesson will introduce the basics of variables in PHP.		Variables, as mentioned briefly in [[Introduction to PHP]], are a significant feature of any programming language. They can be used to store all forms of data, and are generally required to perform multiple manipulations on data not hard-coded into a script. This lesson will introduce the basics of variables in PHP.
			{{ntnes}}
	== Basic syntax ==		== Basic syntax ==
	In PHP, all variables can be identified by the $ at the beginning of their name. Variables name generally start with a lowercase letter, however this can vary for special variables, which will be explained later. To understand how variables work, take this example:		In PHP, all variables can be identified by the $ at the beginning of their name. Variables name generally start with a lowercase letter, however this can vary for special variables, which will be explained later. To understand how variables work, take this example:

wikademia>Wikademia: 31 revisions

2009-04-11T05:41:24Z

31 revisions

← Older revision	Revision as of 05:41, 11 April 2009
(No difference)

205.250.116.93: /* Globals */

2007-11-13T18:10:58Z

Globals

← Older revision		Revision as of 18:10, 13 November 2007
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	===Globals===		===Globals===

	You can force functions to ~~acess~~ other variables by using the global keyword, e.g:		You can force functions to access other variables by using the global keyword, e.g:
	<source lang="php">		<source lang="php">
	<?php		<?php

205.250.116.93: /* Scope */

2007-11-13T18:10:10Z

Scope

← Older revision		Revision as of 18:10, 13 November 2007
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	</source>		</source>

	The page 'another_page.php' has full ~~acess~~ to the variable 'var'.		The page 'another_page.php' has full access to the variable 'var'.
	<source lang="php">		<source lang="php">
	<?php		<?php

wikademia>Baltazart: /* Referencing */

2007-08-29T00:57:21Z

Referencing

← Older revision		Revision as of 00:57, 29 August 2007
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	== Referencing ==		== Referencing ==
	On a sidenote, a less used feature of PHP (and, indeed, many lower level programming languages) is memory address referencing. The idea is that every variable is stored at a certain address in memory. Now, say you wanted to have a variable that always remained the same values as another, you could just store point it at the same address - any changes at that address, i.e. any change to the value of the first variable, would be reflected in the other variable ~~(but not vice versa)~~. Examine the following:		On a sidenote, a less used feature of PHP (and, indeed, many lower level programming languages) is memory address referencing. The idea is that every variable is stored at a certain address in memory. Now, say you wanted to have a variable that always remained the same values as another, you could just store point it at the same address - any changes at that address, i.e. any change to the value of the first variable, would be reflected in the other variable. Examine the following:
	<source lang="php">		<source lang="php">
	<?php		<?php
Line 158:		Line 158:
	$b = &$a; // $b is pointed to $a		$b = &$a; // $b is pointed to $a
	$a = 'Stuff2.0'; // $b is now also 'Stuff2.0';		$a = 'Stuff2.0'; // $b is now also 'Stuff2.0';
			$b = 'Stuff3.0'; // $a is now also 'Stuff3.0';
	?>		?>
	</source>		</source>

wikademia>Ghenson at 13:27, 4 June 2007

2007-06-04T13:27:03Z

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wikademia>Draicone: Simplify

2007-05-05T03:07:33Z

Simplify

← Older revision		Revision as of 03:07, 5 May 2007
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	Variables, as mentioned briefly in [[Introduction to PHP]], are significant ~~for~~ any programming language. They can be used to store all forms of data, and are generally required to perform multiple manipulations on data not hard-coded into a script. This lesson will introduce the basics of variables in PHP.		Variables, as mentioned briefly in [[Introduction to PHP]], are a significant feature of any programming language. They can be used to store all forms of data, and are generally required to perform multiple manipulations on data not hard-coded into a script. This lesson will introduce the basics of variables in PHP.

	== Basic syntax ==		== Basic syntax ==
	In PHP, all variables ~~are denoted~~ by the $ at the beginning of their ~~identifier. They do not need to be declared; they can simply be assigned a value and used from there on~~. Variables name ~~should~~ start with a lowercase letter; this ~~is not required but (in certain php configurations) prevents clashes with autoglobals (~~which will be explained later). ~~Here is a basic~~ example ~~of assigning a value to a variable and printing its value onto the page~~:		In PHP, all variables can be identified by the $ at the beginning of their name. Variables name generally start with a lowercase letter, however this can vary for special variables, which will be explained later. To understand how variables work, take this example:

	<?php		<?php
	$message = '~~This is the value of the message variable.~~';		echo 'Hello world!';
			?>

			Here is the same example using variables instead:

			<?php
			$message = 'Hello world!';
	echo $message;		echo $message;
	?>		?>

	== ~~Variable conversion~~ ==		== Dynamic typing ==
	~~PHP also automagically<!-- NOT~~ a ~~typo~~, ~~please do not change to automiatcally --> switches~~ variable types when needed ~~(for more information on this, see~~ [[~~Wikipedia:Type_inference~~\|~~type inference~~]]~~). For example~~, ~~all~~ strings ~~(a string is a series of characters) must be enclosed in quotes (both single quotes and double quotes are supported). However~~, ~~sometimes values you fetch from external sources will be~~ strings ~~by default but need to~~ be treated as ~~ints (short for integers, which are numerical values) for~~ the ~~purpose of a calculation. This~~ example ~~shows how it can be done~~:		A number of other high profile languages (C and C++, for example) use static variable typing. This means that variables have to be given a data type (e.g. number, string of letters, boolean TRUE or FALSE) that will remain the same until they are destroyed.

			This is often useful, however PHP does away with static typing and dynamically converts variable types when needed. As explained in [[Introduction_to_PHP#Basic_Syntax\|the Introduction to PHP article]], PHP has different syntax for numbers and strings, however due to PHP's dynamically typed nature, strings can be treated as numbers when needed. Take the following example:

	<?php		<?php
Line 18:		Line 26:
	?>		?>

	In this instance, we are multiplying the number 42 (in a string variable) by pi to a certain number of decimal places (a ~~float variable - you will learn about this later~~). Conversion can ~~only occur when possible~~, however - the following ~~will not work~~:		In this instance, we are multiplying the number 42 (in a string variable) by pi to a certain number of decimal places. PHP automatically converts '42' to 42 (a string to an integer). Conversion of clearly abnormal data can produce unexpected results, however. Take the following example:

	<?php		<?php
	$input = '4string2';		$input = '4string2';
	// Should multiply 42 by pi, but will ~~probably post a warning or terminate the script with an error~~		// Should multiply 42 by pi, but will produced unexpected results
	$thevalue = $input * pi();		$thevalue = $input * pi();
	~~// This should return 0 or false, not print anything or even return an error for the previous line~~
	echo $thevalue;		echo $thevalue;
	?>		?>

	As '4string2' ~~is not a number, PHP will fail~~ to ~~convert~~ it ~~(in order to be multiplied~~ by pi(), ~~which returns a floating point value) and~~ (~~most likely) return an error or post a warning (depending on~~ PHP'~~s configuration settings in~~ the ~~php~~.~~ini file~~).		Depending on the PHP configuration, PHP may convert '4string2' to integer values before multiplying it by pi, with unexpected results. (On some PHP versions everything after the '4' is ignored and the result is approximately 12.56)

	== Variable types ==		== Variable types ==
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	* ''float'' - Abbreviation of floating point value. Holds any integer WITH a decimal place, to a certain precision (generally 32 digits)		* ''float'' - Abbreviation of floating point value. Holds any integer WITH a decimal place, to a certain precision (generally 32 digits)
	* ''double'' - Abbreviation of double precision floating point. Same as above except with far more precision - however, a double value also takes up twice as much memory (generally 8 bytes - obviously insignificant on modern servers)		* ''double'' - Abbreviation of double precision floating point. Same as above except with far more precision - however, a double value also takes up twice as much memory (generally 8 bytes - obviously insignificant on modern servers)
	* ''string'' - Holds any array of characters, i.e. a sentence (or two). Generally has an infinite length; however, for compatibility with older servers, limit the size of strings to 32768 characters.		* ''string'' - Holds any array of characters, i.e. a sentence (or two). Generally has an infinite length; however, for compatibility with older servers, limit the size of strings to 32768 characters. Strings are surrounded with single quotes when used in PHP.
	* ''boolean'' - Can either be true or false, many functions return true or false		* ''boolean'' - Can either be true or false, many functions return true or false

Line 60:		Line 67:

	<?php		<?php
	~~var~~ $a;		$a;
	?>		?>

wikademia>Sebmol: Reverted edits by Tooj117 (Talk) to last version by Remi0o using rollback

2007-03-27T20:47:16Z

Reverted edits by Tooj117 (Talk) to last version by Remi0o using rollback

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