Re: C++ Primer exercise 3.13
In article <pan.2007.07.19.11.41.14.495782@gmail.com>,
geek.arnuld@gmail.com says...
[ ... ]
#include <iostream>
#include <vector>
int main()
{
std::vector<int> ivec; /* empty vector */ int v_num;
std::cout << "Please enter some numbers: " << std::endl; while(std::cin
>> v_num)
ivec.push_back(v_num);
Even though it's minutely longer, I'd use an algorithm for this:
std::copy(std::istream_iterator<int>(cin),
std::istream_iterator<int>(),
std::back_inserter(ivec));
Since you're ultimately dealing with the integers in pairs, it might
also be worth considering having a vector of pairs of integers, and put
them into the pairs as you read them. This is likely to make the reading
a little more complex, in the hope of making later manipulation a bit
simpler and (possibly) reflecting the intent a bit more closely.
If you decide to put the ints into pairs, you can cheat a little bit and
set the last one to a pair of the number that was entered along with a
zero in the second item of the pair. This allows you to treat all the
items uniformly from that point onward. Under the circumstances, it may
be more work than is worthwhile, but when you start to deal with more
complex code, the basic concept can be extremely useful.
Creating a vector of pairs could be done something like this:
std::vector<std::pair<int, int> > pairs;
for (int i=0; i<ivec.size()/2; i++)
pairs.push_back(std::make_pair(ivec[i*2], ivec[i*2+1]);
if (ivec.size() %2 != 0)
pairs.push_back(std::make_pair(*ivec.rbegin(), 0);
if((ivec.size() % 2) != 0)
{
std::cout << "oops!, you enetered an odd number of numbers" <<
std::endl;
}
If you're going to leave it as a vector of integers (instead of pairs)
I'd consider removing the last one from the vector at this point, so as
you sum the pairs, you don't have to deal with the possibility of an odd
number of items in the vector.
for(std::vector<int>::const_iterator iter = ivec.begin(); iter !=
ivec.end(); iter += 2)
{
if((iter + 1) == ivec.end())
{
std::cout << *iter << std::endl;
}
else
{
std::cout << *iter + *(iter + 1) << std::endl;
}
}
I prefer to keep the loop clean. The first leg of your if statement can
only ever execute once, just before the loop terminates. In a case like
that, I prefer to deal with that possibility outside the loop, perhaps
something like this:
// N/2 will truncate if N is odd
for (int i=0; i<ivec.size()/2; i++)
std::cout << ivec[i*2] + ivec[i*2+1] << "\n";
// if we had an odd number of elements, print the last one.
if (ivec.size() %2 != 0)
std::cout << *ivec.rbegin();
If you created the vector of pairs, printing out the sums could look
something like this:
struct sum {
int operator()(std::pair<int, int> p) {
return p.first + p.second;
}
};
int main() {
// ... code to read data and put into pairs goes here.
// create and print out the sums of the pairs:
std::transform(pairs.begin(), pairs.end(),
std::ostream_iterator<int>(std::cout, "\n"),
sum());
return 0;
}
--
Later,
Jerry.
The universe is a figment of its own imagination.