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]

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]

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.

 

[Keith Thompson]

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".)

 

[Kenneth Brody]

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 | |
| kenbrody/at\spamcop.net | www.fptech.com | #include <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------------+
Don't e-mail me at: <mailto:[email protected]>