C #else

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Description

In the C Programming Language, the #else directive provides an alternate action when used with the #if, #ifdef, or #ifndef directives. The preprocessor will include the C source code that follows the #else statement when the condition for the #if, #ifdef, or #ifndef directive evaluates to false.

The #else preprocessor directive evaluates the expression or condition if condition of #if is false. It can be used with #if, #elif, #ifdef and #ifndef directives.

Syntax:




#if expression  
//if code  
#else  
//else code  
#endif


Syntax with #elif:




#if expression  
//if code  
#elif expression  
//elif code  
#else  
//else code  
#endif


Note

  • The #else directive must be closed by an #endif directive.

C #else example

Let's see a simple example to use #else preprocessor directive.




#include <stdio.h>
#include <conio.h>
#define NUMBER 1  
void main() {  
#if NUMBER==0  
printf("Value of Number is: %d",NUMBER);  
#else  
print("Value of Number is non-zero");  
#endif         
getch();  
}


Output:

Value of Number is non-zero

Example

The following example shows how to use the #else directive in the C language:




/* Example using #else directive by c programming */

#include <stdio.h>

#define YEARS_OLD 12

int main()
{
   #if YEARS_OLD < 10
   printf("c programming is a great resource.\n");
   #else
   printf("TechOnTheNet is over %d years old.\n", YEARS_OLD);
   #endif

   return 0;
}


Here is the output of the executable program:

c programming is over 12 years old.




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