GATE EXAM PREPARATION IN "C" -macro-preprocessor

#include <stdio.h>
#define square(x) x*x
int main()
{
  int x;
  x = 36/square(6);
  printf("%d", x);
  return 0;
}

(A) 1
(B) 36
(C) 0
(D) Compiler Error


Answer: (B) 

Explanation: Preprocessor replaces square(6) by 6*6 and the expression becomes x = 36/6*6 and value of x is calculated as 36. Note that the macro will also fail for expressions “x = square(6-2)”
If we want correct behavior from macro square(x), we should declare the macro as
#define square(x) ((x)*(x))