The Luhn test in C++11

luhn.cpp

#include <algorithm>
#include <numeric>
#include <iostream>
#include <vector>

/*
 * Assuming an input of a string of digits, perform the Luhn test on the indicated sequence.
 * Returns true if the given string passes the test, false otherwise.
 */
bool luhn(const std::string& seq) {
    static const int m[] = { 0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
    bool is_odd = false;
    auto lambda = [&](int a, char c) {
        return a + ((is_odd = !is_odd) ? c - '0' : m[c - '0']);
    };
    int sum = std::accumulate(seq.rbegin(), seq.rend(), 0, lambda);
    return 0 == sum % 10;
}

int main (void) {
    auto t_cases = {"49927398716", "49927398717", "1234567812345678", "1234567812345670"};
    auto print = [](const std::string & s) { std::cout << s << ": " << luhn (s) << std::endl; };
    std::for_each (t_cases.begin (), t_cases.end (), print);
    return 0;
}