Conditional directives may be used to assemble certain statements
and exclude others. They may be used anywhere in the assembly
program, but are most often used inside macros.
The general syntax of conditional assembly directives is
Each conditional assembly directive ends with an ENDIF and there
can be an optional ELSE clause present. If Conditional evaluates
to true, the Tstatments are assembled, otherwise Fstatements
are assembled if the ELSE clause is present.
The next table gives the forms of the most useful conditional
directives and what is required for them to be evaluated
|Form || TRUE IF
|IF exp || Constant expression exp is nonzero.
|IFE exp || Constant expression exp is zero.
|IFB < arg > || Argument arg is missing (blank). Angle brackets are required.
|IFNB < arg > || Argument arg is not missing (not blank).
|IFDEF sym || Symbol sym is defined in the program (or declared as EXTRN).
|IFNDEF sym || Symbol sym is not defined or EXTRN.
|IFIDN < str1 > < str2 > || Strings str1 and str2 are identical (Case sensitive).
|IFIDNI < str1 > < str2 > || Strings str1 and str2 are identical (Case insensitive).
|IFDIF < str1 > < str2 > || Strings str1 and str2 are different (Case sensitive).
|IFDIFI < str1 > < str2 > || Strings str1 and str2 are different (Case insensitive).