Exer03_24.cpp

// Page 105, exercise 20
// Tips: Some situations must be considered carefully.
// For example: What if the vector is null? What if the vector has only one
// element?
// Here using iterator is easier to prevent buffer overflow than subscript.
// *********************************Key Points*********************************
// Type of an iterator isn't the type of element in vector. If I try to
// substitute int* for auto below, like this:
// int *j = v.begin();
// compiler will throw an error. And from error info we can see clearly what the
// type of an iterator is.
// ****************************************************************************
#include <iostream>
#include <vector>
using std::cout;
using std::cin;
using std::endl;
using std::vector;
int main()
{
    vector<int> v;
    int i;
    while(cin >> i)
    {
        v.push_back(i);
    }
    auto j = v.begin();
    if(v.begin() != v.end())
    {
        if(v.size() == 1)
            cout << *v.begin() << endl;
        else
        {
            for(auto j = v.begin(); (j + 1) != v.end() && j!= v.end(); ++j)
            {
                cout << *j + *(j + 1) << " ";
            }
            cout << endl;
        }
        auto f = v.begin(), b = v.end();
        for(--b; f <= b; ++f, --b)
        {
            if(f < b)
                cout << *f + *b << " ";
            else
                cout << *f << " ";
        }
        cout << endl;
    }
    else
    {
        cout << "No elements!" << endl;
    }
    return 0;
}