Using #else preprocessor directive with C

#else preprocessor directive in C is used with #if preprocessor. When the expression of #if is not true then the code under #else will be executed. Here we will see the syntax and C program using this preprocessor directive.

You may have seen our previous guide about #if preprocessor directive. The syntax of #else is given bellow with #if preprocessor.

// syntax of #else preprocessor directive

#if condition
  //code to execute when #if condition is true
  
#elseif condition
  // code to execute when #elseif is true
  
#else
  // execute the code if above condition is false
  
#endif

C program using #else preprocessor directive

The program bellow will execute the code bellow the #else preprocessor as #if is not true here. Let’s see the program bellow;

// C program using #else preprocessor directive

#include <stdio.h>
#define SYSTEM 1

int main(){
#if SYSTEM == 0
  printf("SYSTEM value is = %d\n", SYSTEM);
#else
  print("SYSTEM value is non-zero.\n");
#endif
return 0;
}

Output of program :

SYSTEM value is non-zero.