How to identity processor architecture

Hi Dear,

I just wanna to know my processor architecture(32bit or 64 bit) through 
c programming.

According to me the sizeof of pointer will give the result. Like below 
coding.

int main()
{
   int *ptr;
   printf("%d",sizeof(ptr));
}

Please correct me if i am wrong...

Any suggestion or help would be appreciated.

Thanks,
Prabhu