Help:Extension:Variables

As taken directly from the extension page on MediaWiki:

Variables is a MediaWiki extension that allows you to define a variable on a page, use it later in that same page or included templates, change its value, possibly to a value given by an expression in terms of the old value, etc.

It is much like a template, only very lightweight and scoped to only a single page, so you can use many variables on a page without slowing down the wiki with huge numbers of templates. Combine this extension with the ParserFunctions extension for best results.

#vardefine


Assigns the value specifiedvalue to the (already existing or hereby introduced) variable variablename.


 * Example: making iconwidth = 25

#vardefineecho


Works exactly as, but the affected value is printed.


 * Example: making iconwidth = 

Retrieving the value of a variable (#var)
The value of the variable variablename is produced by

If undefined, this produces an empty string; it does not give an error message.

It is possible to define a value for the case that the variable is undefined or void:

This is equivalent to:

but it is much shorter and better arranged. Before version 2.0 though, the default value always was expanded. From version 2.0 on the default only gets expanded in case it really is being needed.

The value can be used in parser functions, etc.

#varexists

 * returns 1 if the variable is already defined (also when the value is a void string). If the variable is not defined the return value is void.

#var_final
Experimental new function introduced in Variables 2.0. This function will output the final, last value a variable has at the end of the page rendering. Naturally, the value will be inserted after the parser went over the entire wiki markup, so this function can't be used in other functions, expecting the right value is being used. Example:

The default value will be used if the variable doesn't exist at the final page rendering stage or if its value is an empty string. The default will be expanded right where the function is used, so the parameter will be expanded, even if it won't be needed.

Examples
The ParserFunctions extension must also be installed to use #expr

Compute :

Add one to n: