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32 lines
1.5 KiB
Markdown
32 lines
1.5 KiB
Markdown
[$LET]($LET) is a precompiler command, which is now usable by modern day [cavemen](cavemen) to help include and exclude which sections of code compiles in their program based on OS/bit-size or other predefined conditions.
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## Syntax
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> [$LET]($LET) variable = expression
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## Description
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* Unlike [LET](LET), [$LET]($LET) is not optional.
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* $LET A = 12 sets a precompiler variable "a" to the value of 12. This variable is only valid for the precompiler itself and does nothing to affect the values of any variable/constant which might also be called "a" in the program.
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* Variable names must follow QB64's variable naming conventions.
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* You can check a precompiler variable against special values **DEFINED** and **UNDEFINED**, in order to assess whether the variable has already been assigned a value. Useful for code in libraries which may be repeated.
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* The precompiler comes with some preset values which can be used to help determine which code blocks to include/exclude. These are:
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* **WIN** or **WINDOWS** if the user is running QB64 in a Windows environment.
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* **LINUX** if the user is running QB64 in a Linux environment.
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* **MAC** or **MACOSX** if the user is running QB64 in a macOS environment.
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* **32BIT** if the user is running a 32-bit version of QB64.
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* **64BIT** if the user is running a 64-bit version of QB64.
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* **VERSION**, which is set to the version of the QB64 compiler.
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## Example(s)
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* See example 1 in [$IF]($IF).
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## See Also
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* [$IF]($IF)
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* [$ELSE]($ELSE)
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* [$ELSEIF]($ELSEIF)
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* [$END IF]($END-IF)
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* [Cavemen](Cavemen)
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