How does this code find the center element in a vector?

[The Fearless Hyena]

The book I'm using tells me this code that makes an iterator point to the center element in a vector. I've been trying to figure out how it works though.

int main()
{
	std::vector<int> iVec;
	int input(0);

	while (std::cin >> input)
		iVec.push_back(input);

	std::vector<int>::iterator center = iVec.begin() + iVec.size() / 2;
	
	std::cout << *center << std::endl;

	return 0;
}

[andywestken]

Is that code copied exactly from your book?

If so, I'd burn the book! The loop on lines 6-7 will only break if you force an error by entering a non-numeric value, which is bad form.

If you understand what iVec.begin() and iVec.size() do, you should be able to figure out how the iterator to the middle is obtained.

Andy

[EwCjE3v7]

@andy

No, you can use ctrl+d on linux or ctrl+z on windows, nothing bad in that loop. It'll just stop until eof or if it fails.

[The Fearless Hyena]

Actually I think I got it now. Let's say there is 5 elements. begin() points to the first one that is index 0.

I assume size() would have the value 5 since that's how many elements there is; but wouldn't that make the division by 2 rely on truncation since iterators don't have floating points?

0 + 5 / 2 would be 2.5, truncate it to 2, and you have the center element.

But since 0 doesn't really do anything couldn't we just use iVec.size() / 2?

[andywestken]

@Fr0zen1

Oops - forgot about ctrl-Z

But still think it's a poor form.

Andy