C | Macro & Preprocessor | Question 2

#include <stdio.h> 
#if X == 3 
    #define Y 3 
#else 
    #define Y 5 
#endif 
  
int main() 
{ 
    printf("%d", Y); 
    return 0; 
} 

What is the output of the above program?
(A) 3
(B) 5
(C) 3 or 5 depending on value of X
(D) Compile time error

Answer: (B)

Explanation: In the first look, the output seems to be compile-time error because macro X has not been defined. In C, if a macro is not defined, the pre-processor assigns 0 to it by default. Hence, the control goes to the conditional else part and 5 is printed. See the next question for better understanding.

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