[C++11] Average (short)

#include <iostream>
#include <algorithm>
#include <iterator>

int main(){
    int n = 0;
    std::cout << "Please insert a sequence of numbers! (an invalid input stops the request)" << std::endl;
    std::cout << "The average is: " << static_cast<double>(std::accumulate(std::istream_iterator<decltype(n)>(std::cin), std::istream_iterator<decltype(n)>(), 0, [&n](decltype(n) a, decltype(n) b){++n; return a + b;})) / std::max(n, 1) << std::endl;
    return 0;
}