HP SunSoft Pascal 4.0 - Manual (Page 277)

Pascal Preprocessor 253
A
Syntax
%ifdef expression %then
.
.
%elseifdef expression %then
.
.
%endif
Comments
If the expression in %ifdef expression %then is false , pc skips over the
%then part and executes the %elseifdef part instead. expression consists of a
conditional variable and the optional boolean operators, and , or , and not .
See the %else listing for examples of expression.
Example
The Pascal program, ifdef.p ,
which first checks if bird1 has
been defined. If not, it defines it
with a
%var directive. If bird1
has been defined, the program
checks whether or not it needs
to define
bird2 .
program ifdef_example(output);
%include 'bird.h';
begin
%ifdef not(bird1) %then
%var bird1
%elseifdef not(bird2) %then
%var bird2
%endif;
%if bird1 %then
writeln('Bird one is a ', a, '.');
%elseif bird2 %then
writeln('Bird two is a ', b, '.')
%endif
end. { ifdef_example }