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.
