https://www.codeeval.com/open_challenges/39/

_happy_numbers.cpp

#include <iostream>
#include <sstream>
#include <fstream>
#include <vector>
#include <numeric>

#ifndef __APPLE__
#include <algorithm>
#endif

#define to_string(x) dynamic_cast<ostringstream &>\
    ((ostringstream() << dec << x)).str()

using namespace std;

void square(int& i) {
    i = i * i;
}

void square_digits(vector<int>& digits) {
    for_each(digits.begin(), digits.end(), &square);
}

unsigned int get_new_number(vector<int>& digits) {
    return accumulate(digits.begin(), digits.end(), 0);
}

void replace_digits(vector<int>& digits, const int& number) {
    digits.clear();

    string digits_str = to_string(number);

    for (size_t x = 0; x < digits_str.length(); x++) {
        digits.push_back(static_cast<int>(digits_str[x] - '0'));
    }
}

int is_happy_number(const int& number) {
    vector<int> digits;

    replace_digits(digits, number);
    square_digits(digits);

    while (1) {
        unsigned int new_number = get_new_number(digits);

        if (new_number == 4) return 0;
        if (new_number == 1) return 1;

        replace_digits(digits, new_number);
        square_digits(digits);
    }
}

int main(int argc, char *argv[]) {
    if (argc < 2) return -1;

    ifstream datafile(argv[1]);

    string line;

    while (getline(datafile, line)) {
        if (line.length() < 1) continue;

        int number;
        istringstream number_str(line);
        number_str >> number;

        cout << is_happy_number(number) << endl;
    }
}

data.txt

1
7
22