Scope of macros in C?

Question

How these macros are evaluated?

# define i 20
void fun();

int main(){
  printf(\"%d\",i);
  fun();
  printf(\"%d\",i);
  return 0;
}

void fun(){
  #undef          


        

Answer 1

There's no scope involved at all. Macros are handled at the preprocessing stage separately and independently from the compilation stage and have no concept of a C scope. Your examples could just as easily be:

#define i 20

void fun();

int main()
{
  printf("%d",i);
  fun();
  printf("%d",i);
  return 0;
}

void fun()
{
}

#undef i
#define i 30

And:

#define i 20
#undef i
#define i 30

void fun()
{
}

int main()
{
  printf("%d",i);
  fun();
  printf("%d",i);
  return 0;
}

You can see from those why it behaves the way it does.