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by Dinesh Thakur

The conditional directives are meant to control the compilation process. By using them we may conditionally include certain statements of the program for compilation. If the condition is not met the statements are not included. These directives also help us not to include duplicate files in the program and cause error. For example, see the following code:

 
by Dinesh Thakur

A macro may be used in the definition of another macro as illustrated below.

 
by Dinesh Thakur

Macros may also be created by #define. Here the identifier can have parameters but types of parameters are not mentioned.

#define identifier(parameters) replacement_text

 
by Dinesh Thakur

The token # single in its own line is null directive. It is simply neglected by compiler. Thus, if the code is simply as given below, it is neglected by the compiler.

 
by Dinesh Thakur

The directive #define is used to create symbolic constants and macros (small function type entities). The directive #define may be used in the following manner: