C Programming #define? [duplicate]

Question

Possible Duplicate:
Could anyone explain these undefined behaviors (i = i++ + ++i , i = i++, etc…)

#include<stdio.h>
#include<conio.h>

#define SQ(x) x*x

void main()
{
   int a1 , a2;
   int b1 , b2;

   a1 = 2;
   a2 = 2;

   b1 = 0;
   b2 = 0;

   b1 = SQ(a1++);
   b2 = SQ(++a2);

   printf("Frist = %d",b1);
   printf("Second = %d",b2);
}

I know what is the output of the code.

as #define work in other programe that way it is not working in above code Why.?

Answer 1

The result of an expression with more than one ++ operator on the same variable is officially an undefined behavior in C.