cardinal.cc

/**
 * Integer to Cardinal converter (unsigned)
 *
 * Copyright (C) 2021 Ayan Shafqat <ayan.x.shafqat@gmail.com>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 **/

#include <array>
#include <cmath>
#include <iostream>
#include <sstream>
#include <string>

namespace {
std::string cardinal(long num) {
  static const std::array<std::string, 20> unit{
      {"zero",    "one",     "two",       "three",    "four",
       "five",    "six",     "seven",     "eight",    "nine",
       "ten",     "eleven",  "tweleve",   "thirteen", "fourteen",
       "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"}};
  static const std::array<std::string, 10> ten{{"", "ten", "twenty", "thirty",
                                                "fourty", "fifty", "sixty",
                                                "seventy", "eighty", "ninety"}};
  static const std::array<std::string, 8> weight{
      {"", "thousand", "million", "billion", "trillion", "quadrillion",
       "quintillion"}};
  std::string res{};

  if (num >= 1000) {
    auto ex =
        static_cast<long>(floor(log10(num))) / 3;  // Get engineering exponent
    auto val = static_cast<long>(pow(10, ex * 3)); // Get value
    auto msd = num / val;
    auto rem = num % val;
    res += cardinal(msd);
    res += " ";
    res += weight[ex];
    res += rem ? (" " + cardinal(rem)) : "";
  } else if (num >= 100) {
    auto msd = num / 100;
    auto rem = num % 100;
    res += cardinal(msd) + " hundred";
    res += rem ? (" " + cardinal(rem)) : "";
  } else if (num >= 20) {
    auto rem = num % 10;
    res += ten[num / 10];
    if (rem != 0) {
      res += "-";
      res += unit[rem];
    }
  } else {
    res += unit[num];
  }
  return res;
}
} // namespace

int main() {
  std::cout << "Enter an integer to convert it into words (e.g. 256 -> two hundred fifty-six)" << std::endl;

  do {
    std::string line{};
    std::getline(std::cin, line);

    long num{0};
    std::stringstream ss{line};

    if (!(ss >> num))
      break;

    std::cout << num << " -> " << cardinal(num) << std::endl;
  } while (true);

  return 0;
}