HP SunSoft Pascal 4.0 Uživatelský manuál stáhnout pdf (Strana 277)

100

101

Pascal Preprocessor 253

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 }

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