Hi,
Actually eh, the issue isnt quite settled. On AIX 5.3 I cut and paste
your program and the output is 9 not 10 for the pre-increment. I
compiled the program with xlc without passing any compiler options.
jbase 5 on the same server using the same compiler gives a result of
10 for the OP's code. What am I missing?
0001 #include <stdio.h>
0002
0003 int main(int cnt, char * argc[])
0004 {
0005 int c;
0006
0007 c = 3;
0008 printf("Expr is %d\n, c is %d\n\n", ++c + ++c, c);
0009 c = 3;
0010 printf("Expr is %d\n, c is %d\n\n", c++ + c++, c);
0011
0012 return 0;
0013 }
Expr is 9
, c is 5
Expr is 6
, c is 5
Chenai.
On Sep 5, 9:57 pm, "Jim Idle" <[email protected]> wrote:
> Greg,
>
> Thank you for your proof of Fermat's last theorem, your mistake is at line
> 6.
>
> I have been trying to teach you C for so long now that I cannot remember how
> long it is, but if this is an example of how much you have learned, then
> perhaps I spent about 20 minutes on your lessons? Run the program I attached
> and not your incorrect program. Mine confirms that cnt is 5 and that
> therefore the expression is 10, which your C program is merely confirming.
> as well as confirming that one should not try to write C at 9PM on a Sunday
> after a few beers and a curry. unless you are me.
>
> If a prior version of jBASE did not return 10 in this instance then it was
> incorrect. In fact, I think I remember fixing this bug in 4.x (and
> specifically only at the major point release). or maybe I don't. Perhaps you
> remember me doing this. nah, it was more than 20 minutes ago ;-) (c.f. The
> Invisible Gorilla)
>
> Anyway, your program is evaluating the expression and storing it in the
> variable 'res', but then your printf statement is outputting the value of
> cnt (I think you are missing a letter perhaps? =:?o), which as cnt is has
> been incremented twice by then, will, as you acidulously demonstrate, have
> the value 5, thus proving that C thinks that 3 +1 +1 is 5.
>
> So, you have fallen for the same issue only worse, in that the ++var will
> always happen before the binary operator + and so this will be 5 + 5 = 10.
> However your mistake is even worse because you are not even printing out the
> correct variable. If you are having trouble typing in the program that I
> attached to my email in the first place, then please let me know, so I can
> show you how to type in October when I am back in London. I was going to
> visit with you of course, but I am not sure if I should be associating with
> junior C programmers ;-)
>
> Now, it could well be that the original parser at some point in 3.x did not
> have the correct precedence on the pre_increment operator and so it gives
> the wrong answer. However, the answer that the OP is getting from the latest
> jBASE is the correct one.
>
> In future my eld padwan, you should concentrate on handing out the res due
> to your old master, otherwise you risk looking like a
>
> As I presume that pointing out that your C program is utter crap and merely
> verifies my much cleverer program, I take it that this is sufficient
> demolition of your argument and that you will now be buying the second and
> third rounds as well as the first, as well of course being.
>
> Yours respectfully, etc etc,
>
> Ben Franklin.
>
> From: [email protected] [mailto:[email protected]] On Behalf Of
> Gregory Cooper
> Sent: Sunday, September 05, 2010 12:13 PM
> To: [email protected]
> Subject: RE: Pre-increment
>
> Jim me eld mucker,
>
> All very well and good, but ..
>
> On jBASE 3.x, the answer given is 9 (and then 15 for the second test). This
> is what Xze (??) was expecting and differs to what he saw on jBASE 5.x ,
> answers of 10 and 16.
>
> So no matter what your argument, the fact we get different answers on
> different jBASE releases shows that something is wrong. As you were
> responsible for the jBASE 3.x compiler and not for the jBASE 5.x compiler, I
> would obviously expect the jBASE 3.x answer to be correct ;-)
>
> You then talk about "reference this in C if you don't believe me". Now, not
> as though I didn't believe you or anything, but writing a simple C program
> on Suse 11.2 gives this
>
> main()
>
> {
>
> int cnt , res ;
>
> cnt = 3 ;
>
> res = ++cnt + ++cnt ;
>
> printf("cnt = %d\n",cnt);
>
> }
>
> cnt = 5
>
> So that doesn't match up with either of the jBASE releases or what you had
> said about C.
>
> So there is obviously some behaviour that is hard to pin down with these pre
> and post increments.
>
> I am sure I am missing something here, and await your demolishment of this
> email to prove you right again ! ;-)
>
> Greg
>
> From: [email protected] [mailto:[email protected]] On Behalf Of
> Jim Idle
> Sent: 02 September 2010 17:11
> To: [email protected]
> Subject: RE: Pre-increment
>
> This is correct, reference this in C if you don't believe me. Technically it
> is because the operator is unary right associative and is 'pre' increment.
> Hence, the instruction set generated is (roughly):
>
> INC CNT in place ; CNT is now 4
>
> INC CNT in place ; CNT is now 5
>
> LD CNT ; 5
>
> ADD CNT ; Add 5
>
> And the answer is 10. I presume that you can derive the sequence for your
> second example from this.
>
> Now contrast that with 'post' increment.
>
> Jim
>
> #include <stdio.h>
>
> int
>
> main(int cnt, char * argc[])
>
> {
>
> int c, c1;
>
> c = 3;
>
> printf("Expr is %d\n, c is %d\n\n", ++c + ++c, c);
>
> c = 3;
>
> printf("Expr is %d\n, c is %d\n\n", c++ + c++, c);
>
> }
>
> From: [email protected] [mailto:[email protected]] On Behalf Of [
> Xze ]
> Sent: Wednesday, September 01, 2010 5:35 AM
> To: [email protected]
> Subject: Pre-increment
>
> Hi all!
>
> My question pertains to the way that jbase treats pre-increments
>
> Consider the following routine:
>
> 0004 PROGRAM MY.MATH
> 0005
> 0006 CNT = 3
> 0007 RES = ++CNT + ++CNT
> 0008
> 0009 PRINT 'RES = ':RES
> 0010 RETURN
> 0011 END
>
> The output result is RES = 10
>
> if i change line 007 to RES = ++CNT + ++CNT + ++CNT,
> then the output result is RES = 16
>
> Can anybody explain this behaviour? (I expected the first case to output RES
> = 9 and the second RES = 15)
>
> My system configuration:
>
> OS : AIX 5.3
> jbase : Major 5.0 , Minor 20 , Patch 0364 (Change 85159)
>
> Regards
>
> --
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