Preprocessor Directives in C




C - Preprocessor Directives - Definition and Usage

  • In C Language preprocessor is more or less the own language which can be a very powerful tool to the programmer .
  • All the preprocessor directives or commands begin with “#” .
  • Below is the list of preprocessor directives that C language offers .
C Preprocessor

C Preprocessors #define - Definition and Usage

  • In C Language, the #define directive allows the definition of macros within your source code.
  • These macro definitions allow constant values to be declared for use throughout your code.
  • This macro defines constant value and can be any of the basic data types..
 C Preprocessors #define

C Preprocessors #ifdef - Definition and Usage

  • If the value of expression is true, then the code that immediately follows the command will be compiled.
  • “#ifdef” directive checks whether the particular macro is defined or not.
C Preprocessors #ifdef

C Preprocessors #ifndef #endif - Definition and Usage

  • #ifndef exactly acts as reverse as #ifdef directive.
  • If particular macro is not defined, “If” clause statements are included in source file.
  • Otherwise, else clause statements are included in source file for compilation and execution.
  • #endif’ always matches the nearest ‘#ifdef’ (or ‘#ifndef’, or ‘#if’).
  • Also, we cannot start a conditional group in one file and end it in another.
  • The number of necessary #endif directives changes according to whether the elseif or #else directive is used.
C Preprocessors #ifndef #endif

C Type Casting - Definition and Usage

  • In C- Programming the type casting is used to convert the variable from one datatype to another data type, after we perform casting the variable datatype will be changed.
  • “stdlib.h” header file supports all the type casting functions in C language programing.
C Type Casting


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