Explain working of the code

varadharajan · 02-09-2010, 12:25 AM

What will be the output and how?

Code:

int main()
{
	int a=2,b;
	b=++a+--a;
	printf("%d %d",a,b);
}

zacs7 · 02-09-2010, 12:29 AM

Undefined. And how? As per the C standard of course.

varadharajan · 02-09-2010, 12:31 AM

What is undefined?

zacs7 · 02-09-2010, 12:33 AM

The expression:

Code:

b = ++a + --a;

See c-faq undefined behavior (Make sure you READ the page).

varadharajan · 02-09-2010, 12:35 AM

I'm a new bee. Please help me to understand the working.

varadharajan · 02-09-2010, 12:36 AM

Ok. Thank you for your kind reply.

zacs7 · 02-09-2010, 12:37 AM

You couldn't have read that page in 2 minutes.
There is no answer to spoon feed (not that I would anyway), it's undefined.

kille6525 · 02-09-2010, 04:46 AM

so your preincrimenting a and then predecreminting it as well.... They make it undefined because its just bad programing behavior. And it is considered dangerous code. try this one out.

Code:

int i = 0;
int k = 0;
int j = 0;
if(++k > j || i++<k || j++ == k)
{
  printf("%d, %d, %d",i , j, k);
}

what do you think the output will be? Are teacher used this on a test and the majority of us got it wrong.

**laserlight** · 02-09-2010, 04:50 AM

Quote:

Originally Posted by kille6525

what do you think the output will be?

The output will be 0, 0, 1.

Quote:

Originally Posted by kille6525

Are teacher used this on a test and the majority of us got it wrong.

That just means that the students did not know their stuff or were careless

The code is perhaps a little obfuscated, but the result of the expression is well defined.

zacs7 · 02-09-2010, 02:51 PM

Quote:

Originally Posted by kille6525

They make it undefined because its just bad programming behaviour.

That's certainly not why.

02-09-2010, 12:25 AM	#1
varadharajan Registered User Join Date: Jul 2009 Posts: 4	Explain working of the code What will be the output and how? Code: int main() { int a=2,b; b=++a+--a; printf("%d %d",a,b); }
varadharajan is offline

02-09-2010, 12:29 AM	#2
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,295	Undefined. And how? As per the C standard of course. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
zacs7 is offline

02-09-2010, 12:31 AM	#3
varadharajan Registered User Join Date: Jul 2009 Posts: 4	What is undefined?
varadharajan is offline

02-09-2010, 12:33 AM	#4
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,295	The expression: Code: b = ++a + --a; See c-faq undefined behavior (Make sure you READ the page). __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
zacs7 is offline

02-09-2010, 12:35 AM	#5
varadharajan Registered User Join Date: Jul 2009 Posts: 4	I'm a new bee. Please help me to understand the working.
varadharajan is offline

02-09-2010, 12:36 AM	#6
varadharajan Registered User Join Date: Jul 2009 Posts: 4	Ok. Thank you for your kind reply.
varadharajan is offline

02-09-2010, 12:37 AM	#7
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,295	You couldn't have read that page in 2 minutes. There is no answer to spoon feed (not that I would anyway), it's undefined. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
zacs7 is offline

02-09-2010, 04:46 AM	#8
kille6525 Registered User Join Date: Feb 2010 Posts: 6	so your preincrimenting a and then predecreminting it as well.... They make it undefined because its just bad programing behavior. And it is considered dangerous code. try this one out. Code: int i = 0; int k = 0; int j = 0; if(++k > j \|\| i++<k \|\| j++ == k) { printf("%d, %d, %d",i , j, k); } what do you think the output will be? Are teacher used this on a test and the majority of us got it wrong.
kille6525 is offline

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