How To Use Variables

This function allows you to define a variable on a page, use it later in that same page, change its value, possibly to a value given by an expression in terms of the old value, etc. 
It's much like a template, only very lightweight and scoped to only a single page, so you can use many variables on a page without polluting the wiki with huge numbers of templates. 
*This function requires the Variables Extension be installed. 
== Assigning a value to a variable ==
=== #vardefine ===
:{{#vardefine:variablename|specifiedvalue}}
assigns the value specifiedvalue to the (already existing or hereby introduced) variable variablename.
=== #vardefineecho ===
:{{#vardefineecho:variablename|specifiedvalue}}
works exactly as #vardefine, but the affected value is printed.
== Retrieving the value of a variable (#var) ==
The value of the variable variablename is produced by
:{{#var:variablename}}
If undefined, this produces the empty string; it does not give an error message.
It's possible to define a value for the case that the variable is undefined or void:
:{{#var:variablename |defaultvalue}}
This is equivalent to:
:{{#if: {{#var:variablename}} |{{#var:variablename}} |defaultvalue}}
but it's much shorter and better arranged.
The value can be used in parser functions, etc.
== #varexists ==
:{{#varexists:variablename}} 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.
==Examples==
: Note that the ParserFunctions extension must also be installed to use #expr
Compute 2*a + b:
:{{#expr:2*{{#var:a}}+{{#var:b}}}}
Add one to n:
:{{#vardefine:n|{{#expr:{{#var:n}}+1}}}}
Category:Help