7 replies to this topic

[Chinmoy]

here is a really simple program to swap 2 numbers without using a third variable.

say you have 2 numbers a and b;
now what you do is add a in b.
then save b-a in a.now save b-a in b.


{
int a=3,b=2;
cout<<"Initially to "<<a<<" "<<b;
{
b+=a;
a=b-a;
b=b-a;
}
cout<<"Swapped to "<<a<<" "<<b;
}

take care of the sequence.b takes a+b. now we put b in a by a=(b-a);meaning a=b(initial value).so now a=b-initial.so b=b-a..
simple.

[Chinmoy]

try to do this with pointers..

[broncoslb]

I like it....thinking outside the box

[dcs]

This is not so much of thinking outside the box as it is thinking like we're in the 70's. This is an unoptimization that exhibits undefined behavior.

[Walle]

dcs said:

This is not so much of thinking outside the box as it is thinking like we're in the 70's. This is an unoptimization that exhibits undefined behavior.

Is it?

What behavior is undefined?

What would you say is a smarter way to do it?

[dcs]

Walle said:

Is it?

What behavior is undefined?

When signed arithmetic over/underflows, the behavior is undefined.

Walle said:

What would you say is a smarter way to do it?

The obvious way, using a temporary.

[Walle]

Ah, I get it.

How about unsigned behaviour on overflow? Always wrap or is it also undefined?

[dcs]

Unsigned integer overflow is well-defined as wrapping.