[[$LET]] is a precompiler command, which is now usable by modern day [[cavemen]] to help include and exclude which sections of code compiles in their program based on OS/bit-size or other predefined conditions.


{{PageSyntax}}
: [[$LET]] variable = expression


{{PageDescription}}
* Unlike [[LET]], [[$LET]] is not optional.
* $LET A = 12 sets a precompiler variable "a" to the value of 12.   This variable is only valid for the precompiler itself and does nothing to affect the values of any variable/constant which might also be called "a" in the program.
* Variable names must follow QB64's variable naming conventions.
* You can check a precompiler variable against special values '''DEFINED''' and '''UNDEFINED''', in order to assess whether the variable has already been assigned a value. Useful for code in libraries which may be repeated.
* The precompiler comes with some preset values which can be used to help determine which code blocks to include/exclude.  These are:
** '''WIN''' or '''WINDOWS''' if the user is running QB64 in a Windows environment.
** '''LINUX''' if the user is running QB64 in a Linux environment.
** '''MAC''' or '''MACOSX''' if the user is running QB64 in a macOS environment.
** '''32BIT''' if the user is running a 32-bit version of QB64.
** '''64BIT''' if the user is running a 64-bit version of QB64.
** '''VERSION''', which is set to the version of the QB64 compiler.


{{PageExamples}}
* See example 1 in [[$IF]].


{{PageSeeAlso}}
* [[$IF]]
* [[$ELSE]]
* [[$ELSEIF]]
* [[$END IF]]
* [[Cavemen]]


{{PageNavigation}}