Preprocessors in C programming language

The C preprocessor is a micro processor that is used by compiler to transform your code before compilation.All preprocessor commands begin with a hash symbol (#).

Some of the common C preprocessor directive are :

Directives	Description
#include	Inserts a particular header from another file.
#define	Substitutes a preprocessor macro.
#undef	Undefines a preprocessor macro.
#ifdef	Returns true if this macro is defined.
#ifndef	Returns true if this macro is not defined.
#if	Tests if a compile time condition is true.
#else	The alternative for #if.
#elif	#else and #if in one statement.
#endif	Ends preprocessor conditional.
#error	Prints error message on stderr.
#pragma	Issues special commands to the compiler, using a standardized method.

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