Question

How to use #ifndef #elif #else #endif conditional evaluation in C

Answer 1

#include <stdio.h>
 
#define VAL 3
 
int main(void)
{
    #ifndef VAL
        printf("no\n");
    #elif VAL == 3
        printf("yes = 3\n");
    #else
        printf("no != 3\n");
    #endif
    
    return 0;
}

 
/*
run:

yes = 3

*/

 

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