Recurssion: Why one crashes ?

[codefixer]

Hello:

I am trying to understand why one of these crash while the other works
fine.
long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t--)); //crashes
}

long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t-1)); //works fine
}

Thanks.

[Mike Wahler]

<co*******@gmail.com> wrote in message
news:11**********************@g44g2000cwa.googlegr oups.com...

Hello:

I am trying to understand why one of these crash while the other works
fine.
long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t--)); //crashes
return(t * recurssion(--t));
}

long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t-1)); //works fine
}

The expressions 't--' and 't-1' do not have the same
value. Read about 'post-increment operator' and
'pre-increment operator'.

-Mike

[Peter Nilsson]

Mike Wahler wrote:

<co*******@gmail.com> wrote in message
news:11**********************@g44g2000cwa.googlegr oups.com...

return(t * recurssion(t--)); //crashes

return(t * recurssion(--t));

Both invoke undefined behaviour as they reference t for a purpose
other than to calculate it's new value prior to the next (guaranteed)
sequence point.

--
Peter

[Keith Thompson]

co*******@gmail.com writes:

I am trying to understand why one of these crash while the other works
fine.
long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t--)); //crashes
}

long recurssion(int t)
{
if(t <= 1)
return(1);
else
return(t * recurssion(t-1)); //works fine
}

Add this as the first statement of each function and try running it:

printf("Entering recurssion, t = %dl\n", t);

(BTW, the correct spelling is "recursion".)

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Kenneth Brody]

co*******@gmail.com wrote:

Hello:

I am trying to understand why one of these crash while the other works
fine. [...] return(t * recurssion(t--)); //crashes [...] return(t * recurssion(t-1)); //works fine

[...]

What is the value of "t--" as compared to "t-1"?

For example, given "x = recurssion(37);", what will be the value passed
to the first recursion? What will the first pass to the second? And so
on.

--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
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Don't e-mail me at: <mailto:Th*************@gmail.com>