Undefined values: Difference between revisions

=={{header|PureBasic}}==

Variables are defined through a formal declaration or simply upon first use. Each variable is initialized to a value. PureBasic does not allow changing of a variable's status at runtime. It can be tested at compile-time and acted upon, however, it cannot be undefined once it is defined.

<lang PureBasic>If OpenConsole()

CompilerIf Defined(var, #PB_Variable)

PrintN("var is defined at first check")

CompilerElse

PrintN("var is undefined at first check")

Define var

CompilerEndIf

CompilerIf Defined(var, #PB_Variable)

PrintN("var is defined at second check")

CompilerElse

PrintN("var is undefined at second check")

Define var

CompilerEndIf

Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")

Input()

CloseConsole()

EndIf</lang>

Sample output:

<pre>var is undefined at first check

var is defined at second check</pre>