What exactly does an #if 0 … #endif block do?

Question

In C/C++

What happens to code placed between an #if 0/#endif block?

#if 0

//Code goes here

#endif
         


        

Answer 1

Not quite

int main(void)
{
   #if 0
     the apostrophe ' causes a warning
   #endif
   return 0;
}

It shows "t.c:4:19: warning: missing terminating ' character" with gcc 4.2.4