Question

what does %if mean in c programming

Answer 1

%if

Not much. Most probably a compilation error.

Can you share a code what you're exactly after?

If you're after the if, then it is the branching instruction that allows you to do an action only if a certain condition is met. See more details here.

e.g.:

if (number < 0)
    printf("negative number");
else
    printf("non-negative number");

If you're after the #if, it is a preprocessor directive that enables or disables code segments (some part of the code may or may not be compiled) based on a condition. More details here.

#include <stdio.h>

#ifdef __linux__
#define OS "Linux"
#else
#define OS "Windows"
#endif /* linux */
    
int main()
{
    printf(OS); // This prints "Linux" on OnlineGDB
    return 0;
}