c preprocessor else

by

C #else:

The #else is a preprocessor directive in C which is used with,

  • #if to execute a piece of code, only if the specified condition is FALSE.
  • #ifdef to execute a piece of code, only if the specified macro is not defined.
  • #ifndef to execute a piece of code, only if the specified macro is defined.

 

Syntax:

#ifdef MACRO

// code to be executed if macro is defined

#else

// code to be executed if macro is not defined

#endif

OR

#ifndef MACRO

// code to be executed if macro is not defined

#else

// code to be executed if macro is defined

#endif

OR

#if condition

//  code to be executed if condition is TRUE.

#else

//  code to be executed if condition is FALSE.

#endif

Example:

#include<stdio.h>  
#define AGE 30
void main()
{    
#if (AGE==20)
printf("Value of AGE is correct.");
#else  
printf("Wrong value of AGE.");  
#endif    	 
}

Output

Wrong value of AGE.