C Programming Tutorial
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.