Hi Folks,
If you are writing JBC code and not C, why use a construct that is
so difficult to understand, and obviously returns different
results depending on the environment? Is there a compelling
reason? I realize this is a good discussion of the usage of
pre-increment and quite educational, and that it can be used in
production, but if I'm writing code for a business purpose, I'd
probably use something easier to follow (maintain) and whose
results are more predictable. But, that's just me.
Charlie Noah
The views and opinions expressed herein are my own (Charlie
Noah) and do not necessarily reflect the views, positions or
policies of any of my former, current or future employers,
employees, clients, friends, enemies or anyone else who might
take exception to them.
On 09-06-2010 3:13 AM, Chenai wrote:
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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