What is #else directive in C?
Muhammad AshirThe #else preprocessor directive is used with the #if, #ifdef, #ifndef directives. The preprocessor includes the code in the #else directive if the condition in the #if, #ifdef or #ifndef is not met.
The #else directive must be closed with a #endif directive.
Syntax
#else
/*
your code here
*/
#endif
Code
#include<stdio.h>
int main() {
#if 1 < 0
printf("The code in #if directive is run\n");
#else
printf("The code in #else directive is run\n");
#endif
return 0;
}The code above demonstrates how to use the #else directive.
The conditional expression in the #if directive evaluates to either zero or a non-zero value. If it evaluates to a non-zero value, the preprocessor selects the code in the #if block. If the expression evaluates to 0, the code in the #else directive is run.
The preprocessor passes the selected code block to the compiler for compilation. Together with the #if, #ifdef and #ifndef directives, the #else directive can be used for conditionally compiling certain portions of the source code.
Try changing the expression in the following code to see how conditional compilation works:
#if 1 < 0
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