C Programming

CONDITIONAL COMPILATIONS
These are used to direct the compiler to compile/or not compile the lines that follow

	#ifdef  NULL
	#define NL 10
	#define SP 32
	#endif

In the preceding case, the definition of NL and SP will only occur if NULL has been defined prior to the compiler encountering the #ifdef NULL statement. The scope of a definition may be limited by

	#undef NULL

This renders the identification of NULL invalid from that point onwards in the source file.

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