Split an Integer into its digits c++

Question

I\'m trying to learn c++ on my own and I\'ve hit a bit of a road block. The problem is I need to take an integer,split it into its digits and get the sum of the digits and

Answer 1

I will put an example up in good faith that you will not reproduce it, if this is a homework assignment, use it as a chance to learn...

// reference: www.cplusplus.com
#include 
#include 
#include 
#include 
#include 

using namespace std;

// What does this do?
template 
struct gen
{
  gen(T start) : _num(start) {}
  // Do we need these? But why have I commented them out?
  //gen(gen const& copy) : _num(copy._num) {}
  //gen& operator=(gen const& copy) { _num = copy._num; }
  //~gen() {}

  // Why do we do this?
  T operator()() { T digit = _num % 10; _num /= 10; return digit; }

  T _num;
};

// How is this different to the above?
template 
bool check_non_zero (T i) 
{
  return i != 0;
}

// And this? what's going on here with the parameter v?
template 
T sum_of_digits(T value, std::vector& v)
{
  // Why would we do this?
  if (value == 0)
  {
    v.push_back(0);
    return 0;
  }
  // What is the purpose of this?
  v.resize(_size);
  // What is this called?
  gen gen_v(value);
  // generate_n? What is this beast? what does v.begin() return? where did _size come from?
  generate_n(v.begin(), _size, gen_v);
  // reverse? what does this do?
  reverse(v.begin(), v.end());
  // erase? find_if? what do they do? what the heck is check_non_zero?
  v.erase(v.begin(), find_if(v.begin(), v.end(), check_non_zero));

  // what the heck is accumulate? 
  return accumulate(v.begin(), v.end(), 0);
}

int main()
{
  // What does this do?
  vector v;
  // What is this peculiar syntax? NOTE: 10 here is because the largest possible number of int has 10 digits
  int sum = sum_of_digits(123, v); 

  cout << "digits: ";
  // what does copy do? and what the heck is ostream_iterator?
  copy(v.begin(), v.end(), ostream_iterator(cout, " "));
  cout << endl;
  cout << "sum: " << sum << endl;

  // other things to consider, what happens if the number is negative?
  return 0;
}