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1.5 Conditionals

In a macro processor, a conditional is a directive that allows a part of the program to be ignored during compilation, on some conditions. In the C preprocessor, a conditional can test either an arithmetic expression or whether a name is defined as a macro.

A conditional in the C preprocessor resembles in some ways an `if' statement in C, but it is important to understand the difference between them. The condition in an `if' statement is tested during the execution of your program. Its purpose is to allow your program to behave differently from run to run, depending on the data it is operating on. The condition in a preprocessing conditional directive is tested when your program is compiled. Its purpose is to allow different code to be included in the program depending on the situation at the time of compilation.

1.5.1 Why Conditionals are Used		What conditionals are for.
1.5.2 Syntax of Conditionals		How conditionals are written.
1.5.3 Keeping Deleted Code for Future Reference		Making code into a comment.
1.5.4 Conditionals and Macros		Why conditionals are used with macros.
1.5.5 Assertions		How and why to use assertions.
1.5.6 The `#error' and `#warning' Directives		Detecting inconsistent compilation parameters.