#include <iostream>
#include <string>
using namespace std;

// converts two digit numbers to English equivalent
// Owen Astrachan, 3/30/99

string digitToString (int num)
// pre:  0 <= num < 10
// post: returns english equivalent, e.g., 1->one,...9->nine     
{
    if (0 == num)       return "zero";
    else if (1 == num)  return "one";
    else if (2 == num)  return "two";
    else if (3 == num)  return "three";
    else if (4 == num)  return "four";
    else if (5 == num)  return "five";
    else if (6 == num)  return "six";
    else if (7 == num)  return "seven";
    else if (8 == num)  return "eight";
    else if (9 == num)  return "nine";
    else return "?";
}

string tensPrefix (int num)
// pre:  10 <= num <= 99 and num % 10 == 0
// post: returns ten, twenty, thirty, forty, etc.
//       corresponding to num, e.g., 50->fifty     
{
    if (10 == num)      return "ten";
    else if (20 == num) return "twenty";
    else if (30 == num) return "thirty";
    else if (40 == num) return "forty";
    else if (50 == num) return "fifty";
    else if (60 == num) return "sixty";
    else if (70 == num) return "seventy";
    else if (80 == num) return "eighty";
    else if (90 == num) return "ninety";
    else return "?";
}

string teensToString (int num)
// pre:  11 <= num <= 19
// post: returns eleven, twelve, thirteen, fourteen, etc.
//       corresponding to num, e.g., 15 -> fifteen
{
    if (11 == num)      return "eleven";
    else if (12 == num) return "twelve";
    else if (13 == num) return "thirteen";
    else if (14 == num) return "fourteen";
    else if (15 == num) return "fifteen";
    else if (16 == num) return "sixteen";
    else if (17 == num) return "seventeen";
    else if (18 == num) return "eighteen";
    else if (19 == num) return "nineteen";
    else return "?";
}

string numToString (int num)
// pre:  0 <= num <= 99
// post: returns english equivalent, e.g., 1->one, 13->thirteen
{
    if (0 <= num && num < 10)      return digitToString(num);
    else if (10 < num && num < 20) return teensToString(num);
    else if (num % 10 == 0)        return tensPrefix(num);
    else
    {   // concatenate ten's digit with one's digit
        return tensPrefix(10 * (num/10)) + "-" + digitToString(num % 10);
    }
}

int main ()
{
    int number;
    cout << "enter number between 0 and 99: ";
    cin  >> number;

    if (0 <= number && number < 100)
    {
        cout << number  << " = " << numToString(number) << endl;
    }
    else
    {
        cout << "invalid number entered: " << number << endl;
    }

    return 0;
}