9.5.2 Pre-processing expressions

Pre-processing expressions can occur in #if and #elif directives. The

operators !, ==, !=, && and || are

permitted in pre-processing expressions, and parentheses may be used for

grouping.

pp-expression::

whitespaceopt pp-or-expression whitespaceopt

pp-or-expression::

pp-and-expression

pp-or-expression whitespaceopt || whitespaceopt pp-and-expression

pp-and-expression::

pp-equality-expression

pp-and-expression whitespaceopt && whitespaceopt pp-equality-expression

pp-equality-expression::

pp-unary-expression

pp-equality-expression whitespaceopt == whitespaceopt pp-unary-expression

pp-equality-expression whitespaceopt != whitespaceopt pp-unary-expression

pp-unary-expression::

pp-primary-expression

! whitespaceopt pp-unary-expression

C# LANGUAGE SPECIFICATION

pp-primary-expression::

true

false

conditional-symbol

( whitespaceopt pp-expression whitespaceopt )

When referenced in a pre-processing expression, a defined conditional

compilation symbol has the boolean value

true, and an undefined conditional compilation symbol has the boolean value

false.

Evaluation of a pre-processing expression always yields a boolean value.

The rules of evaluation for a preprocessing

expression are the same as those for a constant expression (§14.15),

except that the only user-defined

entities that can be referenced are conditional compilation symbols.