Re: why Its a Valid Code

From:

"Daniel T." <daniel_t@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 24 Dec 2007 10:00:24 -0500

Message-ID:

<daniel_t-0FB2F7.10002424122007@earthlink.vsrv-sjc.supernews.net>

Pallav singh <singh.pallav@gmail.com> wrote:

In the Given below code Does case const-expression: do not have anny
effect on do ...while(); loop

I suggest you try to (a) modify the code so it can compile in C++, (b)
modify the code so it actually does what you think it should do, then
(c) step through the code in your debugger and see how it does it.

BTW, this is a classic example of using unstructured code as a special
case optimization, don't do this sort of thing by default.

(Unstructured code is any code where there is a jump into or out of the
middle of a loop or conditional.)

#include<stdio.h>
#include<stdlib.h>

int main()
  {

   char to1[] ="Pallav";
   char from1[] = "Puneet";

   char *to = to1;
   char *from = from1;
   int count = 21;

  printf("Value in to is %s \n\n",to);
  printf("Value in from is %s \n\n",from);

  register n = (count + 7) / 8; /* count > 0 assumed */

   switch (count % 8)
   {
   case 0: do { *to = *from++;
   case 7: *to = *from++;
   case 6: *to = *from++;
   case 5: *to = *from++;
   case 4: *to = *from++;
   case 3: *to = *from++;
   case 2: *to = *from++;
   case 1: *to = *from++;
                      } while (--n > 0);
    }

  printf("Value in to is %s \n\n",to);
  return 0;

}