Preprocessor Directives in C
#define cat 10
printf("there are %d cats\n", cat); // Output 1
#ifdef cat
#undef cat
printf("the cats are still here"); // Output 2
#endif
#define cat 10
printf("there are %d cats\n", cat); // Output 1
#ifdef cat
#undef cat
printf("the cats are still here"); // Output 2
#endif