Syntax
#IF test
[#ELSE]
#ENDIF

Remarks

test An expression to test for. The expression may contain defined constants.
Conditional compilation is used to include parts of your program. This is a convenient way to build different files depending on some constant values.
Note that unlike the IF statement, the #IF directive does not expect a THEN.
You may nest conditions to 25 levels.
The use of #ELSE is optional.
Note that #ENDIF must be written as #ENDIF, not as #END IF

See Also

#IF , #ELSE

Example
CONST DEMO = 1 ' 0 = normal , 1= demo
#IF Demo
Print "Demo program"
#ELSE
Print "Full version"
#ENDIF
Since the constant DEMO is assigned with the value 1, the compiler will compile only the line : Print "Demo program" . Code between #else and #endif is not compiled!
When you change the constant DEMO to 0, the other line will be compiled.